but not so sure the 'economic sense' standard of the $54 hopper vs the extra day <$10 holds water.
If so, why does Disney even allow discounts on multiple day passes? Why would they not charge a single flat fee per day per park? Why would they offer an annual pass to someone who can 'save money' by going more than 'x' days a year?
The answer is, as high as the ticket gate prices are, they make their money INSIDE the park, and if you offer an incentive to get into the gates for multiple days, the revenue increases.
The 'sweet' spot is the 5 day mark because it is typical of the American vacation, so you market your base ticket around that, and than tack on 'must have' add ons that that gives you flexibility BUT keeps you on the property for the 5 days..(and buying those $20 mickey ears, those $5 rice kripsy treats, etc.