Not even counting the boss rewards, you also get way less of the normal currency. (Some of that may have been that I didn't go for crit first because I didn't realize it had cheap damage upgrades behind it)
yeah, i think you're totally right that the incentives are a little shaky overall. since each level is harder and gives the player less kills, it will naturally mean a big drop in income as soon as you enter the next level. i'm going to prototype some new strategies to see if there's an elegant solution!