This is really cool! I'd definitely run through a few more races if it was easier to get in and out of the races - the races didn't actually finish properly for me after 3 laps, so I had to restart the game to race again.
I think one change that might be nice is having boost be B/Circle instead of Y/Triangle, or maybe just a trigger - usually I don't really want to let go of the accelerate button to boost, but it's pretty hard to press Y while you're still holding A to accelerate. It's easier to hit both A and X or A and B at the same time though.