We found that DD made a big dent in making the DDP worthwhile. She definitely came out well ahead by the end of our stay. Also, make sure to use your refillable mugs as much as possible - whenever we got back to our resort, DH would go fill our mugs while I unloaded and sorted all our daily shopping/sunblock/et al. I would also go run first thing in the morning while DH started getting DD going.
I HIGHLY recommend looking up the list of snacks that are on the DDP and seeking out the biggest bang-for-your-buck. We let our DD 'splurge' on her snacks last year: Dole Whip, Ice cream sandwiches, and some of the nicer desserts at EPCOT. You will be there over Food and Wine Festival, so there are AMPLE opportunities to get some awesome treats that run $5+ as a snack credit... it's a lot easier to let your girls enjoy a treat like that when you don't have to worry about sticker shock
Another thing we learned is that you get a drink WITH your meal, so if you are eating at the resort, you can fill your mug with a drink, and get a sealed drink from the cooler. We would get milk or orange juice, put it in our resort fridge and then would pay OOP for a muffin or some eggs and bacon in the morning so we didn't use a QS credit and could save it for later.
There are TONS of hints on how to maximize your DDP that are relatively simple - I picked up most on the board. We only decided to do it so that my in-laws wouldn't pick the cheapest items on the menu and would actually ENJOY their meals... we knew we'd be lucky to break even, but in the end we came out far ahead and got to try a variety of fantastic entrees I would never have touched if I paid OOP