I like your idea of a 3-day pass. But as for diminishing returns, I disagree. Sell plenty of $450 APs, I think they could sell a comparable FFP. Those who can't afford it would be reduced to the 3-day pass you propose, which would significantly reduce stress on the event.
It's a lot like trying to explain why DVC is bad for Disney--you have to look at revenue v. expenditure on the part of the resort, ignoring the effect on guests.