That is, indeed, a problem; but it's one that I believe is going to be partially fixed once the building update comes out. The money issue is just one of balance, and again I think that'll be fixed sooner or later as well - once items are valued based on their effects again, we'll be a big step forward there too.
But, on the other hand, I do see what you're saying, and for the most part I agree. I just don't want the 'advancement' of the game to be focused on the PC. I'd stay with expanding your number of buildings - perhaps with better quality ones coming later, perhaps not - and doing something fancy with girls becoming matrons. I don't want to focus on the PC, because frankly that's not the fun part of the game - plus, the scale of the game doesn't really allow it. Slave Maker rightly introduced player stats, but that's because there are really only two important characters in that game (the PC and the girl s/he's training). In this game, the focus is much broader, so focusing too much on one individual wouldn't make sense, to me anyway. However, you really can't give a method of advancement to every girl, either - there are just too many to keep track of. That means you have to compromise, and either focus on a special class of girl (a la SimBroII), or focus on something else entirely. Or both.