I like the idea of adding story. It always adds more weight and personality to the game you're making (which never hurts)! I do not mind improving the graphics for the women in the van.
I would like if a certain amount of money was spent, then we get special kidnapping missions from each vendor. Or if we achieve very simple and attainable milestones (i.e. buy x number of equipment, kidnap x amount of women, and etc) then we get special bonuses (i.e. bondage items, skills, missions, and/or whatever you decide appropriate).