I've found that when I'm not doing character meals, the TIW card is by far the best deal. By deal, I mean not only the cost, but also the freedom to order what you want from the menu rather than what will give you the best "value". When we would do the dining plan, I would think, "since i've bought a meal, why should I eat at the Plaza in MK rather than the GF Cafe, b/c I'm getting a better "deal" eating at GF Cafe."? Even though on that day, I may want just a salad at the Plaza. No way I'm eating "just a salad" at my table service meal. Not to mention feeling like you have to eat those cardboard brownies at the counter service stations b/c it's paid for. I can't tell you how many unopened, melted brownies we've thrown away at the end of a trip, b/c we never got around to eating them all -- but by golly we were going to save them b/c we paid for them.
With the TiW card, I order what I want and only what I want, and if I feel like Surf and Turf at Narcoosee's, I know (1) it's 20% discounted, and (2) I had an $8.00 salad the night before, so a little splurge won't hurt.
If you (and each member of your family) are one of those people who has an appetite to eat the most expensive thing on the menu at each restaurant every day of your trip, the DDP may make sense. The other situation where it makes some sense is if you are doing a lot of character meals. Better to get the $25 buffet for a 4 year old on a meal plan rather than out of pocket. Otherwise -- save yourself the hassle.