We calculated it as well and found that the price was about the same - either 2 TS credits or OOP. We ate at the Coral Reef, which is one of my favorite restaurants at WDW. Nothing on the menu was off limits and we got to choose a app, entree, and dessert along with on non-alcoholic beverage.
We dined on Dec. 23, 2010 and had an amazing, amazing time. The orchestra and chorus brought tears to my eyes. It was breathtaking. I can't remember what seating we had- I think around 6:30 p.m. We lined up about an hour before the show (you have to play this by ear, as it was busy the week of Christmas and also when popular narrators read) and were one of the first (in the dining package line) to get in. No one in the non-dining package got in on our night.
We thought that the reserved seating/sport for Illuminations was not very good and ended up finding an even better place to stand along the lagoon roughly 45 minutes before the fireworks. Have fun! It was one of the more "worth it" dining packages in terms of $ and value, especially when compared to the Fantasmic! package, which I found to be a total waste of money.