Is it more efficient to tax the stock alternator, or upgrade?
 

First off, *flame shield on* I know that electrical loads should be minimized, but I have a burning question: would it be better to tax my stock 80amp alternator or upgrade to a 110amp alt from a larger vehicle (Nissan Quest, in this case.) I know that generally speaking, a higher output alt will cause more parasitic loss, but which you guys think to be greater?

I don't know about this efficiency-wise, but beware of "taxing" them anyway. At least on my Honda, the stock alternator will burn up in short order if overtaxed (such as charging a dead battery.) If you're going to "load up" your alternator, best to upgrade it.

the higher load will cause the alternator to get hotter and die sooner, so you can either choose to swap the alternator or wait until it fails and hope that you can get home.

Keep the stock. The cost of upgrading outweighs the very minimal (if any) efficiency of an upgraded alternator. You'll still pull the same amps. I'd keep the stock til it fails. Cooks choice. Try the upgrade if the alternator is free.

When an alternator is not being asked for power, the only difference between a bigger one and a smaller one is the rotational weight of the rotor and basic rolling resistance of the bearings.

A larger alternator will have larger gauge windings, which will have inherently lower internal resistance at a given output, which will mean slightly more energy efficiency on that side of things - probably enough to balance out the "loss" imposed by its heavier rotating mass.

So... no meaningful reason NOT to do the upgrade, apart from expense if that's a deterrent for you.

It would depend on the efficiency curve of your alternator and the one your considering upgrading too. A larger alternator might have a larger coil current and thus more parasitic drag on the engine. Then again the increased heat on your stock alternator might increase copper losses and drop its efficiency.