Well at 21 I had the same tastes as I do now and back then I would have loved sit down meals every night but there is no way I could afford it. It all depends on what you want to eat. You could eat like a king if you go to the pepper market every day and just get take out so you don't have to pay the tip.
I you are a burger and fries type person it still can be worth it but you just have to do the math.
ex Cosmic Ray's
1/4 pound Cheeseburger $6.59
French Fries $2.49
Beverage $2.49
one meal is $11.59
lets say you get the exact same thing for dinner, not that you will but still it would be $23.14 that isn't counting the drinks you may have at the park.
I know I usualy get at least one beverage in the parks when I go so right there is another 2.50
25.64 in one day eating at counter service one of the cheapest food items inthe park with no dessert. seems like it is worth it the more i think about it lol
Another thing to consider, if you are saving for the trip it may give you peace of mind knowing you won't have to carry much cash in the parks.