You aren't thinking far enough ahead. Right now, that seems silly. Even if I pay for a mountain ride in MK, I'm not paying for IASW. But what happens when you have to pay for mountains, and the best free stuff are the Haunteds and Pirates of the World? Suddenly, people are complaining about never being able to get on there because other people just suck up all the free FPs? Well, now there's a demand for paying for those because it's the only way I can get on there without waiting for 60 minutes.
Those rides aren't as high demand now because the top level rides keep them back in the middle. When the top level rides become even more exclusive, it inevitably pushes up the exclusivity level of the mid-tiers. Once the Haunted and Pirate-level rides get pushed, guess what's next?