It could also be that he just seriously wants your approval about on his project. Maybe he sees you as the coolest relative or friend that he has and he figures what you're doing is working, so.... if it aint broke don't fix it... who knows?
It might help if you work with him a little on his car, and at some point say to him "I wish I had done this and this with my car..." maybe you could be suggestive and encourage more originality that way.
That or find him a better deal on some different wheels. Either way. I say work on it because he's family and sometimes they make great friends.
And now, I need a shot of insulin.....