This is really good! I played it till I got maxed out stats too! Combat felt pretty well balanced, and I really like the auto spawn upgrade idea.
At the end I had a bunch of the lower currencies, though. Have you considered allowing the player to trade x of white for x of green, and so on?
I also noticed the lack of a lose condition, like NeverEndingCircles, but I assumed that since its an idle game, maybe there wouldn't be one? I haven't played many of these, though... Anyway, keep it up! :)