To me, signature restaurants are a much better value on the deluxe plan, for the 2 TS credits it would cost you on either dining plan. The reason for this is that on the deluxe plan an appetizer is included in the 2 TS whereas the app is never included on the basic DDP unless you are at an all-you-can-eat venue where there is either a buffet or some type of salad and/or app served for family-style restaurants.
We still will be sticking with the basic DDP on our July 2010 trip (provided they still have it...hey you never know, Disney changes all the time!). Looking at our dining habits, on a 10-night trip we would do at most 4 character breakfasts, prefer to have a quick CS lunch in the parks so we can enjoy more attractions, and the only 2 credit place we would consider is Hoop Dee Doo, and all the food is included at that dinner show.
We went on a 5-night trip back in July and did the basic, DDP, and paid OOP for 2 character breakfasts. We spent a lot less on food doing it this way than we would have if we had the deluxe plan. Also, for 4 of us on a 5-night trip (only 3 on the DDP as my little guy was only 14 months old), we got 15 snacks total and we had 2 snack credits leftover at the end of the trip. I got some grapes and a Mickey rice krispie treat for the road. I can't even imagine what we would do with 80 snacks on a 10-night trip next time we go (my little one will have just turned 3 and will be on the dining plan). I can't even imagine how we will spend 40 snack credits in 10 days!!!! It sure will be fun though, especially since we will be right by the Boardwalk Bakery and also spending a day in DTD (Goofy's Candy!!!).