The only upgrade you can buy is for the default attack, the others do nothing. Also, the game becomes unplayable once you reach floor 12.
Cute game! Main issues are some enemies give less money than their restraints are worth, the green/yellow/red enemies are super strong, the red enemy will deal bindings even on green health, and the pool being random for ghosts to catch means you might not even see all the ghosts in one playthrough.