We only had the DDP once for 9 days. Did we save money? No probably not but it was close. We did things like Breakfast at Cinderellas Royal Table (2 TS each), Ohana, Crystal Palace, Chef Mickeys, Mama Melrose, and Akershus Royal Banquet Hall (among others). We tried to maximize our "Benefit" Would we have done all this if we didn't have the DDP? Probably not (some of it, yes but not all of it).
It was more about convenience of not having to "PAY" (THERE) for the various events. We were able to pay this off over time as we led up to our vacation as opposed to having all the money at the time of service. It also seemed to make ADRs a bit easier too. We certainly were able to get enough food. It was also nice to let the kids (older) order what they wanted without having to say "No, that's too expensive" which might have occurred had we not done the DDP.
So while the actual cost is a factor, don't forget the value of convenience it brings. As others have pointed out, WHAT you eat will impact the cost/value of the plan, but the value of not worrying about the cost is up there too.