We paid OOP, with a TIW card, for our July trip. We saved 20% off of food, and spent just over $1600 including the cost of upgrading my ticket to an AP, and also including the cost of the TIW card ($75 for AP holders). That wasn't with gratuity or alcohol. I added up the numbers that way to see if we would have done better on the deluxe dining plan. We stayed 10 nights, and there were 2 adults and 2 children, so the deluxe plan would have cost us around $1860. And we would still have to add in the cost of the alcohol we drank, which we got a 20% discount on as well with the TIW card.
We had a total of 18 TS meals (one was CRT, so would have been 2 credits on the dining plan), 1 CS meal at MK for each of us, 1 CS meal at MK just fo each of the kids, 1 CS meal for each of us in DTD, and I got a little something from the quick service place at the Dolphin hotel which doesn't even accept any of the Disney dining plans. We had a total of 24 snacks throughout our trip. We would sometimes share an app and/or a dessert, but DH and I never got our own of either (too much food for us). I even got an app as my lunch at San Angel Inn one day. So, all in all, if we would have had the deluxe plan, we would have been entitled to 30 meals, 80 snacks. We would have used 21 adult meals and 22 child meals, and only 24 snacks. Couldn't have eaten at the Dolphin without paying OOP either. So...we would have had 9 adult meal credits leftover, 8 child meal credits leftover, and 56 snacks leftover at the end of the trip.

Not to mention that we didn't order an app and a dessert each at any of our meals.
So...for us, upgrading to the AP and buying the TIW card works out very well. No guessing if what we order is covered by a dining plan, no guess if the snacks we choose are counted as snack credits, no worrying about using up credits or thinking we threw money away because we weren't in the mood for dessert or an app at that meal. But...for some folks, the dining plan works very well. The basic one worked out perfectly for us on our 2008 trip. We did all -you-care-to-eat dinners so I knew the cost of them before we got the DDP, we did CS lunches, and paid OOP for 2 breakfasts. Plus...DS3 was only 1 year old back then, so he was not on the DDP but we had plenty of snack credits to go around, and when we got CS desserts at lunch, I would get yogurt or something for him to have. Now, we do more TS meals throughout the day, too many for the basic DDP but not enough to warrant the deluxe plan. And we certainly don't do enough CS meals anymore to warrant the basic plan.
As far as going to signature restaurants, yes, we would absolutely go to them paying OOP! We didn't go to any in July because we thought the kids were too young, but we are going to try one with them on our next trip (July 2012), and DH and I will go to one alone one night and put the kids into the kids' camp at the Beach Club resort.