We've done two longish trips - one with the DP and one without.
The first trip, no DP. We ate mainly at counter service places and had no complaints. Wherever we happened to be when we were hungry, we ate. However, I could only spring for one character meal and a couple of inexpensive sit-down meals during the trip.
The second trip, we got a good deal that included the DP. Frankly, with one adult and one child on teh plan, we spent about the same or a bit less than we normally would on food, but what we got was definitely several cuts above what we'd normally eat. First, DD *loved* the fact that we could do mroe character meals. While several sit-down places served us a LOT of food, we ate what we wanted to and didn't try to clear our plates and wind up too stuffed to ride the rides. The one con for me was that you have to have your days planned a lot farther ahead of time so you can make your reservations and then actually get to them - choosing ahead of time which days will be in which parks and then being there so that you aren't in MK suddenly realizing you have 5 minutes to get to AK for your ressie....... Plus, I guess that we did skip getting into some ride lines if I wasn't sure that we'd be back off the ride before the reservation time for a meal, which was a bit of a pain - if we'd not had the DP, wee would have ridden the ride and then grabbed something to eat.
All in all, I think a LOT depends on your travel style. For us, the DP was a great deal, but if we went back, I'd honestly debate whether the timing issues made it worthwhile to buy in again. With a kid in tow, it's nice to have meals pre-paid, but it's also nice to be able to be flexible with our time........