Considering that each hero soul is a 10% DPS increase, doesn't that mean that any ancient you buy or upgrade has to confer at least 10(cost of purchase) in value for it to be effective? Call me crazy, but it means that any more than 2 or 3 ancients, left at low level, is just bad math. Am I missing something that makes buying and leveling ancients better than, say 160% dps increase?
Maybe rather than cycling one by one through the maps, you could let the player choose which map to go to when they prestige? You could also have certain maps gated by things, like prestige over wave 75 to choose Map B, over 100 to choose map B or C, etc. Or unlock maps with one of the currencies in the game, diamonds or rubies? Overall it's a great game!