OP, we are 2 adults who used to use the fdp and never thought about the prices. That aspect of it was great.
However, last year, we decided to try it without the dp. We were a little nervous about it, but decided go give it a try.
We found out that 1) we didn't overeat at each meal just so we could "get our money's worth out of it". 2) We always felt we had to get the most expensive item on the menu with the dp, again to get our money's worth out of it. (a trend starting here?) 3) I was always too full to try the multitude of great snacks and treats at the parks. Felt I was missing out. and 4) we don't travel with kids anymore, so no need for just the 2 of us.
I can see how families can get benefits from the ddp with all the character meals, big eaters, etc.
But for your original question: We saved money without the ddp. We don't eat 3 meals a day. We have a light breakfast, bigger lunch, and then snacks or sharing a small meal for supper. We now have room for all those amazing deserts, treats that we passed up. We don't feel so full from all that eating.
The best thing about oop, is that you are free to eat when you want and where you want. For us, that is the main reason we won't go back to ddp. Lots of times we weren't hungry for Chinese at our appointed adr, and were too tired to travel to epcot just to eat (for an example.) We cancelled many of our reservations because of just not wanting to go to another scheduled adr.
We will never go back to ddp,, even if it is free. There are too many advantages for us paying out of pocket.