Room upgrades is something I have mentioned in the past, and that I still think could be a great addition to the game. When I think of Fallout Shelter (which has a similar room-based building and expanding system), the first thing that comes to mind is how much I hated going through endless levels and floors, trying to look for a certain character. Upgrading rooms just makes sense. Give your break room an extra couch and a TV so the idols can recover more stamina. Buy new equipment for the doctor's office so idols have a smaller chance of needing a hiatus. Rebuild your recording studio to increase single quality and sales. Get your stylist some new outfits and tools so her work yields better results (huge potential for unlockable outfits and styles here. Give the players another reason to level up their stylist and upgrade their room.) Of course, I'm talking about the details here. It's not about literally buying a golden pair of scissors for your stylist or some hot pink IKEA couch for your break room, those examples are just to illustrate the potential of room upgrades. It'll give the players something else to do (upgrading rooms), something to work towards (unlockables and boosts) and will help balance the game's economy (players will spend more money with upgrades).