I believe that you are wrong. I don't believe that lowering prices would bring in so many additional guests that it would increase Disney's profit. The reason that I believe that is because they don't appear to be suffering for customers at the higher price point. If a company can raise prices and still attract a huge amount of customers, then the company has a responsibility to raise prices.Sooner or later Disney will price themselves out. Look at Sears, JC Penny's and KMART. It's a slippery slope. If Disney lowered their prices, in my humble opinion they will attract MORE CUSTOMERS that will buy disney merchandise/food/etc.
I also believe that your Costco analogy was not on point. After all, Costco hasn't kept their membership fees locked in or failed to increase prices on the bulk of their products. They merely have kept the price of a hot dog and soda combo the same. It should also be noted that many would say that the quality of this combo has declined from the Hebrew National dog of yesteryear to the generic dog of today. (Not to mention the whole Coke/Pepsi thing.)