I've thought a lot about this lately. We are going to try it for the first time next month. We normally budget about $100 for food and misc in the parks per day, not including "special" dinners or events. we are two adults and two kids under $10 so for us the dining plan gets us under that amount more or less but with a Table Service dinner every night, something we never did before. It also is A LOT of food. A full lunch with dessert and a full dinner with dessert for every person is definately more than we would get normally so you should consider how much you realy need. The DDP definately favors people that can use that much food.
When my kid turns 10, it goes from $8.95 on this trip to about $40 since he'll be an "adult". LOL, I hope they change this stupid adult age. It may work for theme park rides, but not for food. Anyway, my kids eat very little still so we will NOT be doing the DDP once I have a 10 year old in the mix. This child's price is where most of the financial benefit for us is coming from.
Note: I really don't think the DDP saves that much money now, unless you are big dessert eaters. Previously, it included an appetizer and dessert at dinner AND included Tip. Although I think it is way too much food, that certainly was a better financial "value" but it is easy to see why that was unsustainable. I wish they had dropped the price a little more after taking away those features..oh well.