We've only done the DDP once, in 2008 (I had to go look at my signature - wow can't believe it was 5 years ago!). Only reason we did the DDP was that it was a great deal,
free dining plus a room discount! We ended up doing a couple of buffets (Cape May breakfast, only because we had one table service credit left last day, plus Tusker House which I wanted to do but maybe we wouldn't have without the plan) plus used two credits one night for room service when we were super tired.
My kids liked that they could get snacks or drinks and just swipe their card to buy them, and it was a great deal since it was "free". Many counter service meals are so big that my DD and I would share a meal, and it would be enough. I think we left with a counter service credit or two leftover.
For us, it felt like too much food. I thought about looking into it since, but then the stress of "getting my money's worth" was just too much. I can get by definitely without breakfast (I'm not a huge eater early in the day at all, just coffee and I'm good to go), a light lunch, and sandwich then snack later. Maybe one or two sit down meals is all we need really.
We wouldn't have done the Cape May without having the credit to use up - 4 adults would have been I guess $140? For breakfast - I can buy enough groceries for the room for breakfast and snacks for a week on that. Of course, most folks go to those for the characters - we just were not into that - it was cute - but not what we were interested in.
For someone who definitely wants character dining - yes it can be worth it for sure! Those character meals are expensive.
Side note: my kids and I went last August for 15 nights - stayed offsite (Sabal Palms for the majority of the trip) and only ate one table service meal the whole trip (and that was at Macaroni Grill in Kissimmee). My kids would rather do counter service at the parks, and we also LOVE getting snacks at Epcot. My son loves Japan - chicken terriyaki - that's kind of tradition. When my DH is along (he wasn't that trip) he does like a sit down meal or two, so we'd rather pay OOP for that.
PS: and we do splurge - one of the best meals we've had was at the French Bistro upstairs in France at Epcot - we had the Prix Fix meals with wine pairings, it was incredible, and DH wouldn't even let me see the bill (I know it was well over $400, and that was years ago).
If we ever did a dining plan, it would be the counter service one, but I think they reduced the snacks to one a day from two? Don't know - if it were free and we were staying onsite, I'd do it, but otherwise, if you like character dining and want a lot of sit down meals, it may be worth it.