We did this last September and are considering it again this September...
It is ALOT of food if you eat it all and alot of time in restaurants instead of the other areas of the theme parks, we had dozens of snack credits remaining last year (there were 4 adults) that we used at Goofys Candy shoppe on our last night!....We are going to plan out our trip in the next few weeks. Once we figure out our plan, we'll price out what we'd be paying out of pocket for and then decide whether to upgrade or not.
I really like the convenience of not having to pay for food (just tips etc) while we are there and having a fairly fixed price vacation. For us, we are traveling with my DS who will be 3 during our stay. Since he is still 'free' for the duration of our trip, he doesnt have any meal vouchers so we end up sharing most of our meals with him. For that reason alone we might end up getting the DDDP - so that there is more food to go around! Plus, we cant skip breakfast or just get a cinnamin roll with our snack credit with DS around anymore!