That's a new one on me! There are other reasons for putting a via in the pad, but strengthening a connector is a new one.
The weakest part of an SMD pad is that the copper could delaminate from the fiberglass, and lift off the PCB itself. Anything you could do to prevent that would help, including making the pad larger or putting a via in the pad itself.
But you have to be careful, since putting a via in the pad can cause other issues. The first problem is that it might make the pads not flat enough, so a connector pin won't make good contact with the pad and thus not get soldered well. The second issue is that the solder could get wicked down the via and leave nothing left for the connector pin. This isn't a big issue if you are hand soldering, but can be a problem when doing it with automation.
Honestly, if connector strength is an issue then seriously consider going to a through-hole connector or some type of connector that gets strength from some other means. Maybe a connector that gets bolted to the chassis itself (and stress on the PCB is minimal). Or even a different connector entirely.
SPI bus at 50MHz can easily run a couple of inches thru a few vias without hitch. Wavelength of 50MHz is 6 metres but realistically because fast edges are used you need to think ten times faster. Even so that's a wavelength of 60 cm. Rule of thumb is keep tracks smaller than a half of a quarter wavelength (other folk will use other rules of course) and this means 7.5 cm or 3 inches.
Try and keep clock and data same length and if you hit problems on long stretches you might have to terminate at high frequencies with 10pF in series with 100 ohm (more likely on clock than data).
There is no great theory in my answer, just a whiff of theory and some experiences and he odd rule of thumb. Bottom line - use a ground plane - it's no excuse to say you are not familiar with grounding - get familar - it'll be the difference between something always working and something nearly always never working - it's that big a deal.
Best Answer
Vias in the pads are useful in high speed designs since they reduce trace length and therefore inductance (i.e. the connection goes straight from pad to plane rather than pad-trace-via-plane)
You have to check whether your PCB house can do this though, and it may cost more (via will need to be plugged and plated over to provide a smooth surface) If you can't put the via in the pad, putting directly adjacent and using more than one can help reduce inductance.
They are also useful for Micro-BGA designs, where space is very limited and traditional fanout techniques cannot be used.
A via-in-pad (or capped/plated via) is not to be confused with a "tented via", which is a standard via with soldermask covering the hole (hence "tented")
To illustrate the advantage, here is an example of a TQFP footprint fanout with standard vias and via-in-pads:
It's easy to see why the via-in-pad version is preferable for high speed designs that need to keep inductance low.
The reason it's more expensive is due to the complex process (compared to standard vias) and potential problems (e.g. plating bulging with expansion of plug, or dimpling)
This document discusses various plugging techniques.
Here is a run through of the process: