We went to the Dine with Shamu in April of this year and it was a lot of fun! The food was surprisingly good, at the end of the buffet line, there's a kid buffet with nuggets, mac and cheese, etc...
Here's the link to the menu:
http://seaworldparks.com/en/seaworld-orlando/dine-and-shop/dining/dine-with-shamu/
We did it for lunch and they had us check in at 1:15 (I posted a review on the Dine with Shamu FAQ thread, helped me jog my memory!) and they tell you that the trainer will be out by 2, so we had plenty of time to enjoy lunch.
The big show was going on as we were eating, so you can't see the show. But as soon as the show's over, they bring the whales into the tank right in front of all the tables.
So you eat, then a trainer comes out and tells you all about the whales and then has them do flips and tricks and stuff, it was really cool! My 2 boys loved it!
I definitely think the cost was worth it because when we were there it was hot, so it was nice to sit in the shade and enjoy a leisurely yummy lunch while also getting to see Shamu really close! Plus they take your picture (included in the price) so we got a really nice family shot!
We watched the actual Shamu show later that evening, the last one of the night and it was great!
Have a great time! We loved it and would do it again!