So, I finished all 3 cups and got the cup! :-) But that's all? No additional tracks or game modes or cars?

Now, I look at the bonus tracks and wonder what these are for? The "Super Mud Bowl" is like the other tracks: you can reach the 1st, 2nd or 3rd place. But I don't understand the demolition area. I crash other cars but then I lose. How can I win? I need to "destroy" the other cars, but when I crash into them, my damage meter goes up, of course - until I lose.

You need to hit the other cars to destroy them. The more hits you get by other cars the faster you will die. You need to use your nitro to hit other cars to get less damage. It it possible to win the derby's. You just need to be smart about it. Remember, hitting obstacles also damages your cars.