To single out one point without commenting on the rest:
This in particular makes Sonic even more overpowered in any multiplayer game mode, AND makes speed shoes practically worthless. The one thing that attempts to balance thok in that case is that you can only keep that speed in the air, where you have less control.
My personal opinion on how to solve this is that characters moving above their normalspeed (scaled up for things like speed shoes, to keep those worthwhile) would have less horizontal control than normal. Braking should still be as responsive as always so that they can save themselves, but by gradually reducing the player's ability to turn as they go above their normalspeed, it would add a natural-feeling challenge to maintaining high speed.
I don't mind either way, though. I like the nospin characters being deliberately slower-paced and harder to go fast with than the others, since it gives them a nice contrast.