@CGM - a continuation of the biscuit example, not exactly the same as a limited time retail offer, of course.
I don't disagree with you, but your approach is too simplistic. You can't look at gate expenditure in a vacuum, there is a formula whereby you have to provide value at the gate, to keep per cap spending as high as it is. Merlin thrives on merchandise and other auxiliary spending. If your gate price is too high, auxiliary spending takes a hit because people don't spend as liberally when they're through the gate.
Some people (not all) have a certain amount of money available to them when they visit - you have to find the best way to compartmentalise it and extend the revenue opportunities across various income streams/times of day.
There is a magic number and Merlin and other operators continually try and find what that magic number is by experimenting with different pricing, often using different pricing at their different properties. If it's too low, you run the risk of becoming the cheapest babysitter in town, if it's too high your supplementary income will nosedive.