If the DDP fits your dining style exactly (dessert with every meal, no alcohol, no appetizers) then it's easy to at least break-even with it, and even save money if you work at it.
But quite often, as you've discovered, the TiW discounts are better when you start to eat in a style that doesn't fit the DDP mold. It offers more flexibility. And if you have a larger group, you can easily cover the cost of the TiW card with one or two meals.
If you spend $500 in food and alcohol, you reach the break-even point. And if you have an Annual Pass and can get the cheaper TiW price, your break-even point drops to $375. A group of 6 could easily come close to hitting that point with one meal at a Signature restaurant.
The only time I've ever found that the DDP is a good deal is if it's free at a Value or Moderate resort as part of the Free Dining promos. (But as this thread is on the DVC forum, that's not an option)
-Rob