I think in most cases it's 'snake oil'. all good electronics have the same kind of circuitry built into them to prevent voltage spikes from affecting performance. maybe once in a 100 thousand times it'll save a capacitor or something, but I don't think it's cheap insurance personally.
but I would absolutely encourage you to do your own research on the subject. I just came to the conclusion that no matter what you use there's a risk of damage, and I didn't feel that risk was very high to begin with, so the reduced risk of the pure sine wave, or extra bells and whistles wasn't really the point of the UPS. it was to keep the power flowing long enough to shut down my gear safely, and so far the cyberpower ones have done exactly that for me.
I would think 1000VA's would be plenty for just a projector. but with what I assume your electrician will be doing, i'm thinking the price of the UPS itself won't be the major cost. so if there's anything else you might want to have protected as well, it might make more sense to spend the extra 30 or 50bux to get a 1350VA or 1500VA.
Displays: Samsung PN64F8500/JVC X35
AVR: Pioneer VSX-1130K, 7.1/5.1.2 audio
Sources: HTPC(Enby), PS3, XBOX360, Wii
Control: Harmony One