I wouldn't mind if your vehicle could get totalled (if in a serious crash) and for it to be a pain in the ass to fix, because that would naturally encourage people not to drive like assholes. Also, I would encourage anything that adds role play to the server. It adds frustration, but it also adds another level of risk and role play. Just don't buff police vehicles. (I don't know why I feel that I have to say this). They should break just as easily as any other vehicle. (perhaps adjust damage levels from smallest -> biggest vehicle)
Yeah, maybe it sucks if you're just driving around and happen to crash. But then you're not role playing anyway. I can see this giving cabs more customers as well, for example: if there are no mechanics online. You shouldn't be able to repair your vehicle by yourself though, and not even have mechanic as a second job, because then everyone can just /v get their tow truck and fix it themselves. In that case, what's the point of having this system anyway?
Now, most people can change their own tires and fluids, BUT, if we wanted to add more interaction between players, we could have mechanics have to do that as well. (You'd have to go to a shop to get your tires and fluids changed).