We did the all day dining in December and plan to do it again in April. You can easily get your money out of it, especially ifyou have picky eaters who might take something they don't like, and then they can run back and pick out something else.
However, the only two reasons I hesistate to recommend it:
1. There are also many stands along the paths at Sea World. They sell everything from ice cream/slushies and and 12 oz soda bottles to chex mix and cotton candy. My kids constantly wanted quick drinks and snacks for which you can't use your dining pass. And I don't like 'wasting' more money, so I'd tell them if they wanted something more we'd have to go back to one of the dining pass places for a drink or snack -which took time. Finally I gave in and bought chips and a pop to watch one of the shows but I grumbled about it.

So as long as you are prepared to spend a few more bucks or can say 'no' better than I can.
2. The lines. The lines at the dining pass establishments are hit or miss, sometimes you can walk right up and sometimes you have to wait a long time. And there is no line cutting allowed, or even possible, to just grab a soda refill or anything like that, you have to wait through the whole line again. This also was time consuming. I have to say the cashiers were great about just waving your thru though if you held up your wrist to show your arm band, never had to stand in a long cashiering line.
So just know the pros and cons.