So I've played around a bit... and the fundemental problem is that it's just not worth the time investment to dance/bottle service/ptomote. You can still pretty quickly scale up your milk production/capacity and get exponential growth without too much effort, because thing is? You can only get so pregnant in this game but you can get (almost) infinitely productive milk wise... and worse? If you get into the milk loop it's hard to get out because you need 2x 3x 4x or even more capacity (because dances don't give any? money if you leak) so that you can do other activities without spilling, but if you're in deep that takes a lot of capacity.
You get a bit money doing whatever, then you get as much production as needed to hit cap, then you just keep going, spreading your money between production and capacity (because if you don't have enough capacity you don't make more money from extra production) but even when I was at max size I was getting like $100 per dance which is pennies compared to my milk production and this is at full size too. I think you may either need to put a hard cap on MP and MC (which sounds less fun but might be necessary) or you really start to up the amount of money dancing gives you as your belly size increases.
Because as it stands? I increase my belly size because I want to have larger pregnancies and see the sprites for it. Not because it makes me any appreciable amount of money.
(Side note. If you save/load you get your money but not your upgrades)
(Second side note. If you're going to keep allowing us to up the number of purchases make that number something we can input instead of slowly raise would be great)