I cannot get the math to show a consistent 35% discount by using the Dining Plan unless you go out of your way to order the most expensive items, eat at least 2 sit-down meals each day, and/or re-fill your mug regularly.
Can you really eat over $100 of food every day? It's not so easy.
CA Grill (and most Signatures), Average:
Appetizer - $14 + Entree - $40 + Dessert - $12 + Beverage - $4 = $70
Of course, if you eat at Narcoossee's every night, you could eat $100 in lobster. But beyond that, you need to eat an additional $30/day to get to $100. This requires an additional Table Service meal. Most proponents of the DxDP suggest they do Character Meals to satisfy the need to spend the additional $30 for breakfast or lunch. Like I said, it requires [2] sit-down meals each day to get you to $100 of spending.
The point of DxDP is two or three table service meals per day. If you are going to have a single TS and a QS, you shouldn't bother with DxDP because it will not yield a savings. Likewise, you should like seafood or steaks, because, if you're going to have an entree that is a salad, you're just wasting your money.
For those who are accustomed to eating fine food in sit down restaurants, and abhor quick service food, the DxDP makes sense. I, personally, don't have a problem making and keeping track of ADR's. Having been to WDW 20 times for 7-10 day vacations, I have my favorite places and rides, and don't feel the need to "do everything". I can plan a sit down meal without the guilt of "burning park hours". My sit down meal is just like any other "park experience", albeit usually without waiting 10-90 minutes in line first.
My wife and I keep meticulous track of every receipt, if only to compare them to the tips put on to the KTTW card. The last time we went, a year ago in December, we were averaging $35 per person for lunch, and $75 per person for dinner. At that time, the DxDP was about $80 per person. $110-80=$30 savings. 30/110=28%. There were some days we had savings over 35%, and some days in the low 20% range. But, on average, over 10 days, we saved 28%.
For the forthcoming February 2013 trip, we're at $100/day per person for DxDP. Looking at the latest pricing from recent menus, we expect to spend $40 for lunch and $85 for dinner. That's $125-100=$25. 25/120=21%
In your other post, you also questioned the math of the TIW card. A 10 day pass is $300, not $400. The AP is $611. That's a difference of $311. Using a 20% savings on meals, you'd have to spend $1555 to recoup the difference, plus you'd need to spend $625 to recoup the cost of the TIW card. That's $2175 you'd need to spend on food just to break even. Using my daily spend figures above, you'd start saving after 8.7 days for 2 adults. If you had a 10 day trip, your total savings would be $65 on $2500 of food, or less than 1%. If you had a group of 4 adults, you'd start saving after 4.35 days. With the same 10 day trip, you'd save $565 on $5000 worth of food, or 11.3%. Both of these are typically less than you'd save using DxDP. You stated other benefits of the card, like 10% merchandise discount, and room savings. I don't really buy a lot of merchandise, but the room savings discounts I do use. But, I can get those with the Disney Visa card, or general public discounts. I don't need to buy an AP to get it. If I was a Florida resident, and could use the AP often enough to make it worthwhile, I'd consider the TIW card. But, as I'm not in Florida and stay at Disney resorts, I'm likely to save more using DxDP than your proposed alternative.
