Love the Parlor, already have more than 700 service Exp, and while impregnating my #1 fan/wife, it hit me. What if there was an addiction mechanism?
My thoughts on how it would work would be certain things would build a hidden Exp bar for the addiction (if possible, using the players fetish level as an Exp multiplier), and once you get addicted you need to interact with the girl who gave it. For instance, the breast milk from the demon milf might cause addiction, and once you get addicted and spend a couple segments of time since last consumption, your endurance and strength might get weaker. The longer you go without ingesting/ getting a top off, the worse it gets until you "quit" cold turkey.
This will both incentives and disinterested some interaction, because some people will avoid getting a debuff, while some might take it as an extra challenge. I myself wouldn't mind being hooked on serving a girl, especially if my favorite fan drugged me through either hypothetical kisses or sweat.