An AP can pay for itself in just room discounts that are offered most of the time. There are also quite a few discounts for restaurants, stores at DD and the like.
You don't have to have the AP in hand when you make ressies using the AP discount. All you have to do is produce it when you check in, and sometimes they don't even ask then.
There have been many times when we've ended up saving more than $100/night on our room using the AP discounts.
Just figure out how many days you will be there and how much park hoppers will cost and compare it to the AP. If you eat at sitdown restaurants you can save 10-20% at quite a few of them.
Check out the AllEarsNet web site. It has all the AP discounts, price comparisons for AP vs. PH passes etc.
Hope this helps.