It's not worth it financially if even if not gluten free, it's now just for convenience.
THIS, a thousand times THIS!
As far as gluten-free,
DDP or not won't make much of any difference: you can be confident that at any TS restaurant, you can speak with the chef to find out what gluten-free options they have, and that at CS restaurants, there will be an allergy-friendly menu available to consult.
Now, for the money: I've done the math after our last two trips, and even though we eat wherever we want (including signatures and dinner shows like Hoop-De-Doo), and order whatever meals, beverages, and snacks we want (including steak and seafood), my family of four (with both kids considered Disney "adults" for DDP pricing purposes) saves at least 30% on our dining costs by NOT purchasing the DDP. The only time the DDP would ever be financially worth it for us would be if we got it for "free" as part of a special offer that didn't require us to upgrade our intended room and tickets. (I should add that my daughter is a vegetarian, which does mean that it would be impossible for her to ever order entrees expensive enough to break even on the DDP.)
Not only do we get more flexibility than the DDP would give us in choosing where to eat and what to order, but we still get the convenience of "prepayment," because I purchase discounted Disney gift cards (~9% off, buying them at BJ's at 4% off, with a Discover card, during the months when Discover offers 5% cash back on wholesale club purchases) ahead of time for all of our dining. Whatever money is left on them, we can use for souvenirs. The 30%+ we save on dining over the cost of the DDP doesn't even factor in that 9% savings on the initial gift card purchases! AND we get to enjoy a much higher proportion of table service restaurants than the DDP would cover, including restaurants that would "cost" 2 credits on the DDP (but don't cost twice as much out-of-pocket as comparable 1-credit TS places).
