I really like the idea with the room for Excel's dolls! I'll be sure to add that in the future!
As for the menu sprites, I've been thinking about the same thing too already and I definitely want the sprites to change depending on how much health they have left. As you already said, I will be adding more and more to this feature as the game goes on, since it's really going to be a lot of work.
The idea for wearing costumes at max affection is pretty good! Thank you for that!
also last random thought haha, it would be cool if you could bring one of the slime home after becoming better "friends" with one of them, and maybe they can have a room with rascal for some tentacle fun with your desires :P or just maybe invited for one of the many fun stuff phil does in his room ;p