Here's my .02'
You could take the extra money you save on a hybrid and modify a regular fully loaded Tahoe/Yukon to be getting just about the same MPG's if you adjust your driving habits. Any modification to a hybrid voids the warranty so you can't put different rims on it or anything at all. I looked at them when they first came out and the dealer said as silly as it sounds any modification weather it was taillights or a roof rack would give GM the ability to say that it caused a problem if there was one with the electric motor. So basically if you put new wheels on and the electric motor took a shit GM would not replace it and while that is a bad example because larger wheels could have a huge effect on the motor he had the same response when I asked him about all kinds of mods. So, aftermarket tails.....electric motor takes a shit.....warranty VOID. At least that is what the guy told me. As for me, I couldn't roll bone stock or I would really consider a hybrid, great vehicles just can't do anything to them. You could spend the $10K and put exhaust, supercharger, under drive pulleys, and other performance parts on a fully loaded Tahoe/Yukon and get pretty damn close to Hybrid numbers....just ask JK