I think an explanation for part of the increase in using the ddp has been Disney opening it up to DVC members. I think it was only a year or two ago when we first heard we could now use it. So you are talking thousands of families who had never been allowed to purchase a dining plan suddenly having the ability to also use it. I know we jumped on that train and I'm sure most DVC members also did, and almost all at the same time. Could also explain why the sudden increase in attendance at restuarants.
Not sure I'd agree with you that DVC members getting on the Dining Plan makes a BIG difference. First of all, bear in mind, DDP is still pretty new, they're halfway through their third year. Because it was new, not everyone understood it at first, and many people thought they could eat for less money than what they'd pay on the Dining Plan, which is true, but it requires eating more counter service and less table-service. Once people gradually realized that the Dining Plan afforded them a chance to eat at restaurants they might otherwise chalk up as too expensive, the number of reservations went up accordingly.
Now, my memory may be faulty, but I'm pretty sure before the plan was a year old, they were allowing DVC members to use it, so it happened during the same "breaking in" period I described above.
And because of the annual pass discount, I'm sure many DVC members opt to become Passholders and then get the DDE discount. In my opinion,
allowing annual passholders (whether or not they're DVC) to buy into the Disney Dining Experience probably has more to do with restaurants being crowded, then DVC members being on the DDP.
And with all due respect to "Scooter," when I pick restaurants for my ADRs, I check out the menus, and if I see at least one or two things on the menu I think I'll dig, I make my ADRs. When I'm home, maybe I get all Winnie-the-Pooh-esque and think "now what does my tummy want today?"

But if I go out to dinner, anywhere, it's with the realization of "hey, they'll probably have something with chicken, they'll probably have something with steak, they'll probably have some pasta dishes, some fish..." in other words, there will be SOMETHING I'll want to eat, and in my 37 years on this planet, I'm rarely wrong. Maybe it comes from, oh, I don't know, once being a child and having to eat whatever the hell it was Mom decided to make that night whether or not she asked for my input. But if I'm walking into a restaurant where there are options, I rarely get my nipples in a twist about "but I absolutely have to have chicken fandango, and nothing else will suffice! This restaurant does not serve the one delicacy I must have today, this second, or the terrorists win! This place is evil! EVIL!LLLLLLLL!"