We purchased Annual Passes through
AAA South last summer. 2 adults and 2 kids totaled just under $2600 with the AAA discount. We had to travel to Orlando in December for a short trip, so we decided to make this our Disney year. We will have used about 35 park days (5 trips of various lengths) when our passes expire in June. They are good for 365 days from the date you activate them. (We activated ours in Downtown Disney.) That comes to less than $19 per day per person for us, so it was definitely a worthwhile purchase. We also felt free to relax a little when we visited the parks, knowing we weren't giving up a park ticket day when we just went for a few hours to a park. The freedom to park hop is nice, too.
We also took advantage of the Tables in Wonderland card offer instead of doing
Disney Dining plan. Since we really only eat out for one meal a day and prefer table service over counter service, this has turned out to be a good decision.
Our first trip last summer, we stayed off-property, so having the AP free parking also saved a good deal.
The times we have stayed on-property at resorts, we were able to get AP room only discounts. Even though there is no discount for our upcoming Spring Break stay at the Fort, our other savings have made the AP purchase worthwhile for us.
You just have to compare the numbers and see what works for your plans.