I don't know how I feel about this one. I personally would like such a feature. It's quite annoying to try to drive around and you hit a lampost or something and suddenly your car looks like it's been driven off Chiliad..
It wouldn't really impact gameplay in any way as visual damage and engine health are completely separate.
Making it donator only sounds like a good idea. I don't know exactly how I would go about implementing this. I'd probably just make it something you can do at a gas station I guess..