I really enjoy this game, but one thing you should change is having the gem chance be infinite(like the forge upgrades), an example of how this might work is if you have a 150% rate then you would get one every time, and have a 50% chance of getting a second one. The second part of this change would have to be making this upgrade an exponential curve(a very slow one) so that it would scale to fit later in the game.
let's just say I overlooked it :D