For an adult, the QSDP can be a good deal, and it can be a bad deal. It all depends on where you choose to eat and what you order.
If you're a "big eater" and enjoy getting the biggest item on the menu and a dessert at lunch and dinner, than you'll do fine. If you pick the right places, you'll do great. (Example: Full meals at WPE, Flame Tree, Tangerine Cafe, Cosmic Rays, Sunshine Seasons, and Pepper Market can easily get up to $20 [or more!] with a top-of-the-line entree/combo, drink, and dessert.)
If you're not such a big eater, preferring more basic items and passing on dessert, then you'll be struggling to break even. Ordering kid's meals would be very inefficient. (Just a burger and a soda might work out to about $11 or so after tax. Kid's meals are about $5 after tax.)
The snack credits can make a lot of difference -- the value you get can range from $1 to a little over $4, based on what you get. The shorter the stay, the better deal the resort mug is, too; of course that assumes that you'll actually use it.
As an inbetween approach, if you think it might be too much food, consider planning only two meals a day, and using the desserts (get packaged items whenever possible) as additional snacks. Spreading the food out over the day may make it more worthwhile. If that would work for you, then you can compare costs to see if it's worth it.
There's also the convenience factor of having things pre-paid. It's very subjective -- how much is it worth to you to have that convenience?
Sorry!
