It really depends. How old your children are, are they snackers, do you want to try some of the wonderful sit down restaurants or, when you say on the run, rely on counter service? If your kids are over 6 and you want to have 2-3 sit down than I would say it's worth it, esp if you have snackers who may not devour their whole meal and, two hours later, you're hearing 'mom they have popcorn...I want some poooopcoooorn!' like my kids. With the meal plan you're set as far as your meals go and don't have to keep track of what you're spending where. Plus each of you gets a snack each day. Ice water is free in the parks so you don't have to use a snack option for a drink during the day, if you don't want to.
The plan saved us money since the buffets and TS we ate every night, alone, came really close to paying for our pp cost per day for the ddp. And, if your kids are 9 and under the plan is very reasonable.
Also, I'd probably continue doing it on future trips even if it didn't save us much. The fact that I can pay on it within the package, a little at a time, until we go is very appealing. When I'm making small payments I don't feel it like when I'm having to come up with money all day everyday for food while I'm there. And having to compromise on where we want to eat and how much because of it.