The only general rule of thumb I can think of is to balance loading whenever possible.
In a three phase system, when harmonics are generated at any point, every mitigating measure is some variation of getting them to dissipate as harmlessly as possibly, through or across some kind of reactance. One way of getting them to dissipate is by simply allowing them to flow through devices that are closer to the non linear load than the service entrance. The load creating a harmonic can only supply it so much power, and by sinking that through another load, it doesn't make it's way back to the mains as well. Some harmonics negate entirely when balanced. Occasionally facilities that get in trouble for harmonic generation or effective power factor can get back within limits simply by balancing their phase loading.
Of course, if this is the strategy, then the linear loads near harmonic generators will have to be rated to handle the extra heat generated.
And it seems like a higher per unit impedance would attenuate harmonics leaving or entering a facility; so generally speaking, I suppose it is safe to say that a higher short circuit capacity would allow higher amplitude harmonics simply by not stopping them.
As far as your gigantic light bulb theory, we can reason it out. If they draw the same amount of instantaneous power, then they draw the same amount of instantaneous current, which suggests they have the same impedance at the fundamental frequency. Of course, that impedance will be higher for higher order harmonics, making the motor less effective at harmonic sinking than the resistive light bulb. In reality, though, that light bulb is enormous, AND you need three of them - and you probably don't need that much light. But, maybe this makes a case for placing lighting loads alongside noisy loads?
I suppose the next question would have to be, can a halogen luminaire bulb handle the harmonics?
The most simple and direct answers to the main question depend on how "excessive" it is. Since most equipment is designed to operate within +/- 5% of nominal, the "extra energy" usually gets dissipated as heat, in the device itself. In the case of a light bulb (for example), it produces more light and heat. If the excess energy goes beyond the tolerance of the devices, they will overheat and/or burn (cause damage). These results will be obtained regardless of what causes the "excess energy" on the grid (lightning, solar installations, wind power, etc.).
For the last two questions, if you are charging a 12v battery with a 13v source, the extra 1v will keep the battery "warm" after it is charged to 12v. If you are charging it with an 24v unregulated supply, the battery will overheat, burn up, and possibly explode. If you charge it with an over-voltage and current-limited supply, the battery will be charged to 12v and the extra energy will be dissipated as heat in the supply regulators. One way you can make "efficient" use of any "extra energy," would be to use a bank of batteries and a "smart" charger, which would switch the charging to another battery when one is charged, and shut off (disconnect) when all the batteries in the bank are charged. If there is no interest in saving the extra energy, it can be "dumped" into an appropriate load and converted to heat.
Best Answer
A particular reason why the electricity companies think harmonics are bad is that they have to supply them (which means a generally slightly thicker cable on average) AND they can't usually bill the user for them. There are exceptions of course (for higher energy users) and they are encouraged (by the cost of their bill) to keep harmonics low and power factor as close to unity as possible.
A harmonic is a term that nearly always applies to a non-linear load distorting the normally sineusoidal load current. Basically it's not a higher power consumption but it does mean the infrastructure has to be able to cope with the basic billable currents and the generally non-billable harmonics: -