Will both of your daughters eat their own, adult-sized entree? Or would they split, or one of them order a kids' meal? If either of them would NOT eat an adult-sized entree almost all of them time, then that right there tells me you'll probably lose money on the dining plan.
I haven't added it up, but I just got back from going on a free dining promotion. Even paying to upgrade to the regular
DDP from the QSDP, and forgoing room discounts, it was the best decision for my party, for this trip. That said, I don't think paying for the DDP would have been a good decision for us. We were generally too stuffed to eat dessert after our TS meal, we often ate CSes that we didn't really want because we HAD to, we threw away a TON of food, and we had a number of credits left over at the end of the trip. We find the basic DDP to be TOO MUCH FOOD. (I am not a terribly bird-like eater, either.)
Before our first trip on the DDP, I was a) really excited about having desserts with each meal, as I am a sweets-girl but don't normally order dessert out, and b) concerned about not having enough food, as it just didn't sound like enough. By the end of the trip we were so stuffed that I was sitting at the table going, "No, not another dessert, I can't eat another one!"
So, I don't think I'd counsel a family to get the dining plan, unless they are confident they would really use ALL of it, and be hungry for all of it. If you would eat $47/pp worth of food, every day, in a counter service (entree, drink, dessert,) table service (entree, drink, dessert,) and a snack -- then yes, it makes life easier and I do like the plan. It's kind of fun not to look at the $$$ on the menu and just order what you WANT to eat.