Hey, it's been a few years (we went in January 2004) but we did the dine with Shamu lunch...not with the show. The thing that's with the show is a special seating area and they bring you a box lunch. I don't think that would be worth it at all unless you went on a really crowded day and didn't want to get your seats early, and wanted to eat lunch while watching the show.
Anyway, we did the Dine with Shamu lunch, it's a buffet, so they take you to your seats and a server brings you your drinks but then it's an all-you-can-eat deal with several choices for adults and several choices for kids. It's pretty decent food (mid-to-upscale hotel buffet quality), but what makes it worth it is your seats. You are seated along a border of about six feet separating you from the whales and trainers.
We happened to get what I felt were the best seats in the house, I don't know if it was because I called and booked it in advance or what, but they had the whales doing their training with the trainers right next to us. There were seats that were not nearly as good, further up the holding tank and while the whales probably swam by, they just weren't the same. People were getting up and standing behind our table to take pictures, so I know our spot was one of the best. My three-year-old at the time was a bit intimidated, they were THAT close. I mean, we were "eye to eye with the great beast!" ;-)
You can ask the trainers questions. It's pretty well worth it, I thought, and it's a pretty special experience.
If you have any questions, just let me know. We're going back to San Diego/Seaword/Legoland in April so I'll be poking around here again from time to time.
kim
We had the table right next to the tank so every once in a while we got a little splash but my granddaughter LOVED it 
Great way to start the day and you can ask lots of questions
