Our last trip was the first one we took using the
DDP. Because my DD is severely allergic to peanuts and tree nuts I was always hesitant to use the meal plan. I figured it would be more limiting and she would have to miss out on desserts, since they seem to be the hardest to find safe substitutes.
Long story short, I was pleasantly surprised by the flexibility of Disney. I have been to WDW many times with my food allergic child and been more than pleased about the seriousness with which food allergies are dealt with and with the way Disney chefs will often go above and beyond for my DD (making special desserts, etc.) However, I had my doubts that they would be as willing to go the extra mile with the restrictions of the dining plan. I was wrong.
As I'm sure you've read on related threads, planning ahead is the key. For all sit-down meals, I was sure to make ADR's at places we had already been to or to places where I'd reviewed the menu and found there were more than one option for DD to choose from. At restaurants with no safe dessert, I called ahead and requested either an Itzakadoozie or a Mickey Bar (which were nut-free on our last trip, but not the previous ones) for my DDs meal-plan included dessert. This worked like a charm. In fact, my other DD started to get a little jealous of her sister's desserts. Now that was a first!
As far as the counter service places went, if something on the children's menu was not safe for my daughter, I spoke to the location's manager and appropriate substitutions were made. For example, at the the seasonally open El Pirata y El Perico, the dessert that came with the kid's lunch was a Haagen-Dazs bar that had a chocolate almond coating which my DD clearly couldn't eat. I spoke with the manager and explained my situation. In the course of the conversation I mentioned that the chocolate pudding served at Pecos Bills next door was safe. So, the manager said she could have that and he'd bring it right to our table.
In terms of the DDP saving time, that's a decision you'll have to make based on your family. No question, having one sit-down meal a day is definitely time consuming. And since the advent of the dining plan, you need to make your ADR's 3 months in advance. There will be no spontaneous dinner plans on this vacation. But if you're hesitating because of the food allergies -- don't. In my experience, how Disney handles food allergies is no different for guests on the meal plan and guests who are not.
Have a great trip!
DVCDawn