Here is an idea. Freemium OR Premium versions of the same game.
I don't know how hard this would be, or if Apple would allow it, but why not have 2 versions of some games? I would love to buy that RCT game, but I don't buy IAP. But I would pay $10 for it if the ratings were good. Why can't there just be 2 versions? Since I don't do IAP, they can't make money from me, or the thousands or millions of people who won't do IAP. Seems like they are leaving money on the table to me.