I like the idea, it would even make prevent those annoying players getting in your way and blocking you. But the cars shouldn't be able to run on sidewalks, grass and sands. So it would prevent assholes driving on players for streaks.
Another idea is, you should be able to change the color of your car for 200 gralats or so, and probably have some sort of decals or other stuffs for your car to make it look "cool". Like decorations.