I might have missed it, but I don't think the game came with controls instructions. It would have been nice if the mouse cursor wasn't visible in the play-area.
If you wish to add single player (which definitely will give you more plays) you could either have the window scroll at set pace or do an AI jumper.
The bonus of getting on the spring seems a bit large as the other player will have a hard time ever keeping up.
Other than that, I think you could build a game out of the mechanics.