Nobody has to do it. It's there as a choice - wait in line for "free" or pay extra, skip the line.
I mean, our first night we plan to go to Epcot - if Rat's line is ridiculous and I can buy us each front of the line for $15 each....yeah, we'll do it. I'm not saying I'm asking for paid fast pass, but I am being honest that there are times I would probably buy into it.
I'm part of the problem!
THIS.
Yes, the prices are fairly high. But that's the point. Fastpass+ had very little real benefit, because when you try to let EVERYONE skip the line, you're really not giving a benefit to anyone. It's mostly illusion. Yes, you get to "skip" 1 or 2 lines, but you pay it back in other lines.
The fairly high price will indeed limit the benefit. As you said, you'll do a cost benefit analysis. As will everyone. Prices need to be high enough to discourage the majority of people. You can't sell 30,000 access passes to a ride with a capacity of 10,000 per day.
Those looking at it as, "damn, at $15 per pass, I'll need to spend $600 per day for a family of 4" are missing the point. Yes, you'll have the option of spending $600 per day, just like people have the option of spending $4,000 for a VIP tour.
But most people will do a cost benefit analysis based on their own willingness to wait on a line, their desire for the ride, and their own personal budgeting.
Some people will be willing to spend $20 to skip a 15 minute line to Star Tours. Some people will think it's not even worth $10 to skip a 2 hour line at FOP. The pricing will adjust -- that 15 minute line to Star Tours will see the access price drop to $5-$10, while that FOP 2-hour line skip will jump to $20-$30.
In the end, I suspect
on average, people will utilize it like FP. 2-3 rides per day, that they will pay for. I'm guessing that will be the average... with many guests never paying for a single ride, and some guests paying for 5+.