Grinding extra materials could be interesting. However, I think I would do a couple things:
- Make the car feel heavier. It felt like once I starting going at a certain speed, any little bump was going to flip me over.
- Once you start driving, orient the camera to the front of the car. Unless the player is moving the mouse, in which case it should move relative to the front.
Take these suggestions with a grain of salt. I've never programmed driving a car, so I don't know the difficulties that lie in that process. However, you did a great job on the game.