I think it would be much better if I could pick when I want to level up. As it is currently, leveling up mostly debuffs me due to the speed decrease and makes it impossible to get to new coins. Since leveling is a debuff, it makes only one upgrade make sense(more spikes). Bigger spikes doesn't seem to bring much value when the best strategy is walk backwards and rotate a bit to apply damage.
Cool idea but the core mechanics could benefit from finetuning.