Hey! Sorry for responding so late, it's been a while since I opened my laptop. It's great but are you sure about the chest stuff? I mean, almost all the fun in your game comes from going really fast and killing enemies. I'm not sure that having 2 different ways of upgrading your player is really going to make the game better. The simpler, the better. Having just an upgrade system where you choose between 3 randomly selected upgrades in a pop up menu seems to be a better fit. I mean, it doesn't break the flow of the game and it seems easier to implement.
Again, I'm really no game designer and I might be giving you terrible advice, so trust your gut if you don't like the idea.
Have a great day :)