The calculator at distripplanner.com might be helpful to you, if you have an idea where you might like to eat.
Here's my take (with apologies to Jeff Foxworthy):
Do you plan to eat exactly one counter service meal, 1 table service meal and 1 snack, per day? If so, you might want the DDP.
Do you believe there's an instrinsic value in pre-payment that makes it worth it to prepay, even if it costs a little more in the end? If so, you might want the DDP.
Do you enjoy giant fountain beverages and desserts with every meal? If so, you might want the DDP.
Can you easily find things you enjoy in the entree section of a menu, without requiring any substitutions (e.g., appetizer or salad as your meal)? If so, you might want the DDP.
Are your children all aged 9 or younger, or if any are older, are their tastes and appetite sufficient to be satisfied by ordering from the adult menu every time, at 2-3 times the cost of a child's meal? If so, you might want the DDP.
Do you love the freedom of being able to choose any entree on a menu regardless of price, even if you know that you might "lose money" on your DDP investment if you order less-expensive entrees? If so, you might want the DDP.
Can you limit your restaurant choices to 1-credit table service venues (or are you comfortable eating at 2-credit places, knowing you'll have to pay for an additional meal out of pocket every time you choose one)? If you, you might want the DDP.
We've tried the DDP and it was both convenient and fun, but all we did was "break even" on the cost of things we wouldn't have purchased if we were paying out of pocket, anyway -- the amount of food that went to waste was a little shocking. For my family, the DDP doesn't save us anything -- in fact, now that my son will be over the magical age of 10 on our next trip (meaning he'd be priced as an adult), we'd pay far more for the DDP than we will out of pocket. We also want to try some signature (2-credit) restaurants, which are never a good value on the dining plan. It also doesn't really fit the way we like to eat, if we're ordering what we most want (rather than just trying to choose things that maximize DDP value). I like to drink water instead of fountain beverages, and especially at lunch, sometimes prefer to order a salad or an appetizer or two as my "entree." We never eat dessert except at dinner, and even then, usually order a couple of desserts for our family of four and split them. My son would often prefer to order from the children's menu instead of the adult one, and there are times we just want a hamburger instead of a salmon fillet. Also, we don't all necessarily want a snack every day, and the refillable mugs get used only a time or two. I've used distripplanner and consulted restaurant menus, and if my calculations are correct, we'll save at least $200 this time around by paying out of pocket for 1snack/1TS/1CS per day instead of using the DDP, even with 3 signature restaurant meals. The savings will increase even more if/when my 10-year-old orders some of his CS meals from the children's menu, which I anticipate he'll prefer to do in most cases.