I agree with Non_Newtonian_Games, controls are very good and feels very natural.
And ye, if you would add power ups would be great idea. Because in current implementation the speed of cars is the same and the only thing that helps to win is navigation on the track. But if you expand on this game and will improve enemy AI they probably won't stay in the middle of the track near the turns. Then power ups can bring some strategy - should I get speed or cut the corner...
Same goes to the surface vs stay on track as Non_Newtonian_Games mentioned as well.
Maybe add some win/lose condition.
Also the collisions feel a bit off - I tried to collide from the side and front, they both stop the car and it jitters near the wall. What I would recommend is to give some recoil and reduce the speed, but when bumping from the side you should be able to save more speed.
Good game :)