We've been buying APs for years now and, whilst we have taken advantage of the discounts, for us, the real value is in the flexibility they offer. We frequently dip in and out of the parks, sometimes for very short periods, and APs allow us to do that without feeling we've 'wasted' a day's pass.
Another benefit which hasn't been mentioned yet is that you don't pay for parking - a significant one given that it's now up to $9 a day.