If you decide to upgrade the game after the rating are over, I would recommend you to add different pick ups on the road (probably it's kind of obvious, but anyways). It might be a common element of similar games, but with the random speed feature, it will create a good constant dilemma of "should I go for it or no?" This seems as a funny concept for a mobile game, though, and the fact that the game is more unpredictable, but not random, makes it well balanced. Enjoyed playing your game!