The only way it is worth it is if you manage to book with a tour operator that has the QS plan free for staying at a Moderate or Deluxe resort and then pay extra to upgrade it to the DP. To do this however you have to book early (before the end of October) for a holiday in the following year. We did it this year and it was well worth paying the extra to upgrade as what we "spent" on meals was far greater than what we actually paid for the upgrade from QS to DP. I can confirm that with the DP you only get an entrée and a dessert together with a beverage (which may be alcoholic - beer or wine etc.) for a TS credit.
The way that it works is simple - your account (Magic Band) is credited with the total number of Snacks, QS and TS meals for your whole party for your whole stay and then you can use these however and whenever you want until they have all been used up. For the two of us staying at POFQ or 21 nights we started out with 84 Snacks, 42 QS meals and 42 TS meals available on day 1. Every time that we used a credit for something we received a receipt which showed us what we had used and how many were left.
There are no limits on how much that you can spend - for example the character meals at Crystal Palace, Cape Mays, Garden Grill etc. and the dinner/show packages for Fantasmic and Rivers of Light are all one TS credit/person (unless you choose to eat at a signature restaurant such as The Brown Derby which will use two TS credits/person). Be Our Guest (dinners) and Cinderella's Royal Table (all meals) are two TS credits.