We just did the Fantasmic Dinner Package last week at Hollywood Brown Derby. I believe the cost is approx $37 per adult and $15 per child. This included an appetizer, entree, and dessert for each person. The food and service were wonderful. We have also done the dinner package at Mama Melrose, which is also a GREAT restaurant. I think it is worth it to not have to wait in the crowd to get in and be guaranted a seat. The theater really fills up fast, and we have seen the show several times when it was standing room in the back. The show is incredible. I have also heard people upset that the seats for the dinner package are not centered, but I don't think it really matters because the way the set is laid out, I don't think there is a bad seat in the house. I would suggest making them a few months in advance. You will be asked to secure the reservation with a credit card, which is different from making a priority seating.
Enjoy.