A really solid game!
Some suggestions:
- Instead of (+10) for upgrades, use (>10), which only buys up to the next multiple of 10. (I wish ALL such games used this, as players are more likely to want round numbers.)
- Add (!10) and (=10) auto-upgrade buttons. The first cancelled auto-buy when the ability reaches the next multiple of ten, and the second waits until there is enough saved up to achieve the next multiple of ten all at once.
Cheers!