I'm probably going to be sorry, but...
I have never not broken even on the dining plan, even the trip with the picky vegetarian and counter service (I ate a lot of other people's credits while they got small things OOP). That one we weren't sure we would actually get our value out of but sanity is worth something.
We eat a lot. Constantly. I know it's too much food for some people, but we're always trying to spread those credits out to cover what we want to eat. We do "maximize" but it's not exactly a hardship.
I always try to hang onto my receipts and run the numbers, but some time around dinnertime on the first day, we're obviously ahead and it's become a nuisance. I do, for every trip, run a typical day of what I think we'd actually order and compare it to the dining plan. I also run the value of every "credit", which the family has as a target. If someone wants something significantly under the target, we pay OOP and save the credit. It'll get used later. We've never wasted a credit (a few have become lunch for the road or the train, but that's not a waste).
We're probably good candidates for the DxDP, but but it's enough more up front to pain me, and we don't want to commit to that many table service meals (or tipping on them).
We've taken two trips without DDP. The first one we were offsite in a rented house with a large family group, and it was fine, but we cooked a lot, which isn't my first choice on vacation. The second was offsite, with YES tickets, and a tighter food budget that we had anticipated. We spent less than we would have with the DDP, even QS, but there was a lot of cranky yelling and leaving the World earlier than we wanted to because we were starving and our dinner budget was not going to go very far onsite. It was a miserable experience on what was otherwise a good trip, and a marked contrast to the ones where we ate as much as we wanted and had tasty sandwiches to eat at Georgia Welcome on the way home.
I ran conservative numbers for a sample day for this trip and I have Turf Club--
Prime Rib, Ice Cream, Soda--40.00
Prime Rib, Chocolate Torte, Coffee--42.00
Lamb Loin, Chocolate Torte, Coffee-44.00
WPE--Chicken, Soda--19.00
Salmon, Soda--23.00
BB Wolf Sausage Company--3 Little Pigs, Frozen Lemonade--15.00
Pretzel Braid--6.00 Snack Credit
Snack Credits-Goofy Glacier-4.00
Two Starbucks--10.00
I'm at $203, for a plan I've spent just under $210 for, with two snack credits available, so even at the average of $4 each, I'm ahead without figuring the resort mugs (which we like but wouldn't pay for).
This is, by the way, for what's probably a ticketless trip, so we'll have lots of time to eat. We will pay for a few things OOP, and likely have an evening snack in the room. This isn't everybody, but it works for us. And I do buy Disney gift cards ahead of time to pay for the things we're likely to want that are not on the plan.