Pretty fun little game, the window shake made it pretty easy though. I got a shield coin after stage 2 and just obliterated the rest because I was physically impossible to kill. Still enjoyed it, though, and I hope to see more.
I would say that after you click your first coin, you can't shake again until next turn. This way it will make it more "well, I will work whatever I have here" or "I have to shake more times until the planets align and everything shows what I want it to have". Maybe with a maximum of X shakes so...?