Really fan of this game and management type of games in general. Tremendous potential here. Good enough to actually make me post a reply, lol. Anyway, I don't know if it is already in the works or that it has already been suggested. But you could implement a bit of depth and challenge into the game by adding goals or challenges that you should aspire to reach by a certain day. For example: Reach 50 popularity before Day 20 or Have 5 girls by Day 30 etc. You could have the game potentially 'end' at Day 100 or something and basically give the player a score based on how many challenges he managed to complete during that time. Of course giving the option to continue the game beyond Day 100 aswell if you just want to buy everything there is and finish story stuff with Nicole f.e if you haven't already without having to deal with the game ending at Day 100.
Also having more detailed "book keeping" would be appreciated. Like where the income is coming from? Which girls are making the most money, the maintain costs etc. Right now, there are maintain costs regarding 'mafia' subscriptions and one time purchases, but not much else. I would really appreciate adding girl salary to the mix. More popular the girls, the higher salary she will demand. Now you would have to think about which girls to purchase and at what point in the game, because you don't wanna drive yourself to bankruptcy by buying a expensive girl that demands a high salary which you cannot upkeep. So addition to their purchase cost, the girls take a salary each day based on their popularity. Also you could add rent for the property based on how many upgrades you have bought. More upgraded the club, more it will cost to upkeep. Things like That.
You could also add a 'Game Over' type of situations in that if you're broke (as in you have negative amount of dollars, because of salary and other expenses), you lose the game in like 5 days if you don't correct the course during those 5 days.
Edit: One pretty neat idea I also have is that there could be more things happening to the girls that prevent them from working other than Energy. The girls might get sick f.e. and they need to fully recover in order to get back in action. The chance of getting sick could be based on Energy (the lower the Energy, higher the chance of getting Sick) or have a completely new stat, like Health for example to monitor that. Health could be depleted just like Energy during shows, but obviously other acts like Sex or Group makes the Health loss faster when compared to acts like Dancing f.e. Now the player would have to think about more than just the girls Energy. This would also give the girls individual stats a bigger impact. When you have girls that are good dancers, it is wiser to have them dancing for more cash than have them have sex for potentially less cash and a increased chance of getting sick. Until of course the girls sex stats get better. Also why I would advocate on implementing lessons for increasing individual stats other than openness.
Anyway. Loving the game so far. Especially the gameplay element during the strip shows and the fact that you can add your own custom girls to mix it up. Keep it up!