I read on some forums about a stolen vehicle generating "heat", meaning that it was getting attention from cops. If they had that same concept you could customize your vehicle and it would gain attention of the civilians. Like some people may take pictures of you or the car, or say great things about your car if you are in a completely tricked out or exotic ride, but depending on the neighborhood you are in it could make you more of a target for carjacking or maybe robbery, seeing as how you are supposed to be able to witness other civilians committing crimes. I think that that could put a really interesting spin on what you drive and where.