Hm. My idea is to make difficulty settings that increase boob growth speed at the cost of introducing a max size. In my opinion, simply making the growth speed a slider essentially eliminates the anticipation, as you can just max out the speed, see the huge sizes immediately, and then you have no more enjoyment from the game. Edging is important.
But your comment about the game overs is food for thought. Should I go for a "highscore" mode with game overs, or an endless mode without game overs where your time invested is the only "challenge"?