We got the DDP 3 times pre-2008 when it was just me and 2 kids.
We decided to forgo the DDP for the DDE (which we have used in the past). We spent more money on food even with the 20% discount than if we had used the DDP for less meals out.

Of course, this included wine and other things maybe not included in the DDP.
I called
DVC MS to add the DDP for the second half of the trip (4 nights) when we switched resorts and DH was joining us. I think the DDP savings no longer comes from the TS restaurants but from the CS restaurants. Those meals really add up and there are no discounts available at most of them.
Now I never use to be a CS person. We use to eat most meals at TS and others in the room. But every since Disney added free DME and I tried the DDP program, I have gotten spoiled. No car, no groceries - buy EVERYTHING from Disney. Pre-paid, MORE than enough food - kids, you may get ANYTHING you want that is included.
That being said, I think we might get DDP in the future only if we use DME and if the trip is shorter. If we stay longer or have a car, we will probably stick with the DDE.
BTW, I think that one of the BEST deals for using the CS credits is at the Wolf Gang Puck Express at DTD. It's almost a TS except you order and pay after lining up in the beginning. The meals are served to you on real plate and silverware and the food is much better than the normal CS meals.
WGPexpress participates on the DDP but NOT on the DDP plan. However, you do get 10% off as a DVC member (subject to change of course).
HTH.