Managed to get 21500 Gold and made it to level 15.
Cute little game and quite enjoyable concept. I had fun messing around with a couple different builds. The only thing that really stood out to me was a lack of variety. There's already very few choices for how to upgrade, and having only one enemy really hurts. Even just an enemy who had more health and gave more gold would be interesting, as it would give a greater reason to boost your damage per click, rather than your range (At the moment, every enemy having low health generally means that more then 2 damage upgrades seems like a waste).
Also the play again button doesn't seem to work, but considering you can just refresh the page I don't think that's a big deal.
Fun little game!