Level 33? That's pretty good! The furthest I myself managed to make it is level 40, and I'm planning for it to have 50 levels in total.
As for more modifiers, I've already got 18 of them, and I'm running out of ideas. I'm planning to add one that creates explosions that deal damage in an area, instead of shooting fragments, and another one that lets the player guide the bullets with the mouse.
Removing them with RMB is actually an excellent idea.
Thanks for the feedback!