while skills are trainable to 100% it seems to me that girls without any type of make-up and clothing should not have the ability to reach 100 in beauty or charisma, the two main stats for attracting customers.
hardwired stat maxes to around 80 seems to be working fine with boosters of lipgloss, makeup and pretty dresses that all wear and tear after 3-5 uses with the odd special item that has double the amount and of course cost a proportionate amount more. that will give the incentive of getting those materials in bulk and of course make sure girls are presented best possible.
while torturing will improve the relationship with the owner it will certainly not have a beneficial effect on their looks (bruises and scratches, burnmarks and so on) which only have a very limited appeal to most customers.
also, breeding your own super stock should mean a drop in customer attraction since not all find having sex with a pregnant woman to be the top of their desires. Perhaps impose a longer term of forced inactivity during last 10 weeks before birth?
most games have a tendency to have a "threshold" after which the rest of the game is a sure winner, the size of the win is merely a manner of how much you pool together. it seems to me, the more fame you have and the more girls you can support, the more the local authorities will bleed you. "pay this and this or we'll bust your business"