The idea behind FP as mentioned countless times, was that guests could feel like they are getting more for their money, but actually getting more money out of guests. They do not regret FP being free since in all actuality they are getting that extra FP $ in forms of shops and food $$ spent..
I know if they were to monetize FP like some parks do, it would turn me off of going. I haven't been to Kings Island here in Ohio more than 1 time in last 8 years because my experience with their "fastpass" where people could continue(infinite times during the day for a set price) to cut line because they paid, was so poor.
Every company yearns for something like FP, where you can increase $$ coming into the park, while making people feel like they are able to get more accomplished because of a "free perk".. Monetize FP+ and then they are basically double dipping(FP+ money, and increased shops/food income), and people like me will stop going.
I do miss the old system(paper FP) that lended early birds, and vets a bit of an edge.. but they are a private company who can now give incentive to staying on property with the extended FP window etc.. even if I continue to ask for a portion of FP's to only be available to book day of..