I pushed this game to it's current limits and there's a lot of balancing needed for end game. Mithril and souls are too hard to come by to max the upgrades. I still haven't maxed everything due to this. The balancing issue is clear though as the upgrades need 8 mithril and 6000g. I'm hitting 50,000,000 gold before I get those 8 mithril at this point as it takes so long to progress a single level now. Maybe the mithril and souls you have left over when you prestige could carry over into the next runs?
Great game though. Fresh and fun concept and I like the fact that it is an actual idler that doesn't need constant baby sitting (except for the start, and early mid game when you are rapidly farming artifacts)