I'd like if the level cap of ALL the villains were based on either your level or your place in the story.
For example, I didn't take part in this last promotion at all, because I had to choose between (small chance of points toward new girl, large chance of tiny amount of money) and (guaranteed large pile of money). I picked money.
If the Dark Lord's level cap raises, so that his POTENTIAL level is as high as whatever zone you're on now, I'll always want to take part in the promotions in earlier areas, because then I'm both leveling up the villain (which feels like a kind of player progress) and getting chances at points toward the promo girl AND eventually getting almost as much money on the "bad" rolls as I would if I did my current zone.