Look at it this way. On the DxDP you will have 3 TS meals per day - or one "regular" TS meal and one "Special" (signature, CM, etc) meal per day. At EVERY meal, each person will get an app, an entree, and a dessert. Plus each person will get 2 snacks per day. Ask yourself this question: If you were paying out of pocket, would you order this much food? If the answer is yes, then the DxDP is definately a "good deal".
I have a 7-day trip planned with 6 TS lunches, 1 signature lunch, and 7 signature dinners; I strongly considered the DxDP. DW and I rarely have an app at lunch, and if we do, we share. We never have dessert at lunch. We will typically share an app at dinner, and MAY share a dessert. In round numbers, that's about 20 apps and 20 desserts "included" on the DxDP that we would normally never order. When I "ran the numbers", paying OOP for the way we would "normally" eat. it came out about $400 cheaper than the DxDP. When I added in TIW, the difference went up to around $600.
Also, remember that tips are not included in the DxDP, so, depending on "how big" you order, you could have a $20-30 per adult per day OOP expense (kids would probably be less if they ordered from the kids menus, but that is NOT the way to maximize your "savings" on any DP).
Other factors to consider is how much your room is costing. Rooms that come with the DPs are typically not discounted. There are frequently room-only discounts. Which would save you more money - rack-rate room with DP or room-only discount and dining OOP?
I'm not specifically "down" on the DDPs, but just sounding a word of caution - what sounds like a great deal up front, may not be "as good" as deal when you look at all of the details. For some families, no doubt, it will affect a savings - or at least be worth the "convenience" of having meals (mostly) pre-paid. But it's not a one size fits all, and and if the $$$ aspect is of prime importance to you, you need to really do your accounting before you fall pray to the Disney marketing team...