Hmmm. Besides more levels, it would be fun to have a few more challenging course obstacles (maybe only optional for those that want) like a loop or really long jumps, or maybe a horizontal cylinder that rotates so you have to roll forwards and sideways to cross it. I guess more variety in obstacles is what I'm saying. The player can really move quick and it was fun trying precision jumps from the tops of the towers to a tiny platform on the other side of the level.
I don't think I'd remove anything, but maybe move the stats from being always next to the player to a traditional UI element. It was a bit annoying to have to rotate my view to see how many diamonds/speakers I hadn't found yet, and I kept seeing it and thinking I was seeing a diamond I had missed, only to realize it was the diamond on the stats card lol.