Proper bypassing and grounding are unfortunately subjects that seem to be poorly taught and poorly understood. They are actually two separate issues. You are asking about the bypassing, but have also implicitly gotten into grounding.
For most signal problems, and this case is no exception, it helps to consider them both in the time domain and the frequency domain. Theoretically you can analyse in either and convert mathematically to the other, but they each give different insights to the human brain.
Decoupling provides a near reservoir of energy to smooth out the voltage from very short term changes in current draw. The lines back to the power supply have some inductance, and the power supply takes a little time to respond to a voltage drop before it produces more current. On a single board it can catch up usually within a few microseconds (us) or tens of us. However, digital chips can change their current draw a large amount in only a few nanoseconds (ns). The decoupling cap has to be close to the digital chip power and ground leads to do its job, else the inductance in those leads gets in the way of it delivering the extra current quickly before the main power feed can catch up.
That was the time domain view. In the frequency domain digital chips are AC current sources between their power and ground pins. At DC power comes from the main power supply and all is fine, so we're going to ignore DC. This current source generates a wide range of frequencies. Some of the frequencies are so high that the little inductance in the relatively long leads to the main power supply start becoming a significant impedance. That means those high frequencies will cause local voltage fluctuations unless they are dealt with. The bypass cap is the low impedance shunt for those high frequencies. Again, the leads to the bypass cap must be short else their inductance will be too high and get in the way of the capacitor shorting out the high frequency current generated by the chip.
In this view, all your layouts look fine. The cap is close to the power and ground chips in each case. However I don't like any of them for a different reason, and that reason is grounding.
Good grounding is harder to explain than bypassing. It would take a whole book to really get into this issue, so I'm only going to mention pieces. The first job of grounding is to supply a universal voltage reference, which we usually consider 0V since everything else is considered relative to the ground net. However, think what happens as you run current thru the ground net. It's resistance isn't zero, so that causes a small voltage difference between different points of the ground. The DC resistance of a copper plane on a PCB is usually low enough so that this is not too much of a issue for most circuits. A purely digital circuit has 100s of mV noise margins at least, so a few 10s or 100s of μV ground offset isn't a big deal. In some analog circuits it is, but that's not the issue I'm trying to get at here.
Think what happens as the frequency of the current running across the ground plane gets higher and higher. At some point the whole ground plane is only 1/2 wavelength across. Now you don't have a ground plane anymore but a patch antenna. Now remember that a microcontroller is a broad band current source with high frequency components. If you run its immediate ground current across the ground plane for even a little bit, you have a center-fed patch antenna.
The solution I usually use, and for which I have quantitative proof it works well, is to keep the local high frequency currents off the ground plane. You want to make a local net of the microcontroller power and ground connections, bypass them locally, then have only one connection to each net to the main system power and ground nets. The high frequency currents generated by the microcontroller go out the power pins, thru the bypass caps, and back into the ground pins. There can be lots of nasty high frequency current running around that loop, but if that loop has only a single connection to the board power and ground nets, then those currents will largely stay off them.
So to bring this back to your layout, what I don't like is that each bypass cap seems to have a separate via to power and ground. If these are the main power and ground planes of the board, then that's bad. If you have enough layers and the vias are really going to local power and ground planes, then that's OK as long as those local planes are connected to the main planes at only one point.
It doesn't take local planes to do this. I routinely use the local power and ground nets technique even on 2 layer boards. I manually connect all the ground pins and all the power pins, then the bypass caps, then the crystal circuit before routing anything else. These local nets can be a star or whatever right under the microcontroller and still allow other signals to be routed around them as required. However, once again, these local nets must have exactly one connection to the main board power and ground nets. If you have a board level ground plane, then there will be one via some place to connect the local ground net to the ground plane.
I usually go a little further if I can. I put 100 nF or 1 μF ceramic bypass caps as close to the power and ground pins as possible, then route the two local nets (power and ground) to a feed point and put a larger (10μF usually) cap across them and make the single connections to the board ground and power nets right at the other side of the cap. This secondary cap provides another shunt to the high frequency currents that escaped being shunted by the individual bypass caps. From the point of view of the rest of the board, the power/ground feed to the microcontroller is nicely behaved without lots of nasty high frequencies.
So now to finally address your question of whether the layout you have matters compared to what you think best practices are. I think you have bypassed the power/ground pins of the chip well enough. That means it should operate fine. However, if each has a separate via to the main ground plane then you might have EMI problems later. Your circuit will run fine, but you might not be able to legally sell it. Keep in mind that RF transmission and reception are reciprocal. A circuit that can emit RF from its signals is likewise susceptible to having those signals pick up external RF and have that be noise on top of the signal, so it's not just all someone else's problem. Your device may work fine until a nearby compressor is started up, for example. This is not just a theoretical scenario. I've seen cases exactly like that, and I expect many others here have too.
Here's a anecdote that shows how this stuff can make a real difference. A company was making little gizmos that cost them $120 to produce. I was hired to update the design and get production cost below $100 if possible. The previous engineer didn't really understand RF emissions and grounding. He had a microprocessor that was emitting lots of RF crap. His solution to pass FCC testing was to enclose the whole mess in a can. He made a 6 layer board with the bottom layer ground, then had a custom piece of sheet metal soldered over the nasty section at production time. He thought that just by enclosing everything in metal that it wouldn't radiate. That's wrong, but somewhat of a aside I'm not going to get into now. The can did reduce emissions so that they just squeaked by FCC testing with 1/2 dB to spare (that's not a lot).
My design used only 4 layers, a single board-wide ground plane, no power planes, but local ground planes for a few of the choice ICs with single point connections for these local ground planes and the local power nets as I described. To make a long story shorter, this beat the FCC limit by 15 dB (that's a lot). A side advantage was that this device was also in part a radio receiver, and the much quieter circuitry fed less noise into the radio and effectively doubled its range (that's a lot too). The final production cost was $87. The other engineer never worked for that company again.
So, proper bypassing, grounding, visualizing and dealing with the high frequency loop currents really matters. In this case it contributed to make the product better and cheaper at the same time, and the engineer that didn't get it lost his job. No, this really is a true story.
Think of the high frequency currents that are running accross the ground plane.
At low frequencies, the current follows the path of least resistance (literally). A island in the ground plane isn't much of a issue in terms of resistance. There is still plenty of copper on either side of the island so that the current can flow around it with little voltage drop.
However, things look different at high frequencies. The high frequency return currents in the ground plane tend to follow the same path as the forward currents on the other layers. This is a useful property since it minimizes the total current loop area, and thereby it radiates less and the loop is also less susceptible to incoming radiation. Islands in the ground plane force currents to go around them, which may significantly increase the loop area of high frequency currents. Looking at this another way, you can think of the conductors on the top layer as forming a transmission line with the ground plane. Island break this transmission line, which increases the impedance, which increases the voltage drop accross the ground plane.
Another effect is something known as a "slot antenna". This is the inverse of a dipole, but behaves just like a dipole for radiating and receiving. If you have high frequency current running down the length of a conductive sheet and then cut a slot in that sheet perpendicular to the current flow, you have a slot antenna. This is one reason that air flow holes in metal chassis are usually a bunch of holes, not slots or single large openings.
On a two layer board, you usually have to route some of the signals onto the bottom layer. But, you want to leave the bottom layer a ground plane to the extent possible. From the analysis above, you can see that more small islands is better than few large ones. The metric you want to strive for is to minimize the maximum dimension of any island.
I use Eagle and its auto router often for such things. In the first few routing passes I set the costs just to find a routing solution. In later passes I assume a solution has been found and now it needs to be optimized for least damage to the ground plane. To get that, I set the ground plane layer cost high and the via cost lower. That results in more short "jumpers" in the ground plane layer instead of long traces. Unfortunately Eagle still tends to clump these jumpers together, even with the hugging parameter set to 0. After the final auto route, I manually clean up the ground plane a bit. This is usually not changing the topology, but mostly separating individual jumpers from each other so that there is copper flowing between them.
Here is the bottom layer drawing of such a board:
This shows the bottom layer of our USBProg PIC Programmer. A circuit of that complexity can't be routed on a single layer, but note how there are lots of individual small islands instead of long traces or large clumps of jumpers in the bottom layer. For the most part, the high frequency return currents can still flow without too much deviation from their ideal paths.
Best Answer
If your sense circuit is well designed (high input impedance say > 1K- and good common mode rejection) it should be quite insensitive to resistance in the sense lines, so matching is not required and the resistance of the vias and traces is of little importance. Of course it would be better in general to use parts with four connections but your method probably is pretty good.
Cutting the ground plane may have other effects, especially if high current traces cross the cut, but sense lines should not be affected.
Trace width is of little importance if your sense circuit is well designed, but you may wish to keep them close together (specifically minimize the loop area of the differential input) to minimize susceptibility. Usually the circuit is quite low impedance due to the shunt resistor source so it's not really that critical.