Played to around level 21 or 22? Lost track :) I agree about the "Outrun the void" concept, it's a cool idea but doesn't seem to have any effect. It would be better if there was a way to both gain and lose ground -- maybe each time you Flip you lose a *tiny* bit of momentum and have to build up your speed again, so if you flip too many times you get overtaken, and conversely maybe when you get a star -- or alternatively there might be items in the game that simply speed you up or slow you down a bit.
Great concept, simple & hypnotic, great work!