I did it this past January at the Brown Derby and it ended up being a great deal because I think we paid less with the package. I can see why you wouldn't want to go with kids though, the food is geared more toward adult tastes. We were allowed to order off the whole menu: appetizer, entree, dessert and still only paid $39 per person TOTAL, when I think it would have been about $50+ per person without the package. If you were going to eat at Brown Derby anyway, it's a great deal. I may try it in May with Mama Melrose, so I can try a new restaurant.
Not having to wait a looong time for Fantasmic was nice too. Even in January on a cold night, it was PACKED in there. I believe we arrived about 30 minutes before the show started and still got great seats in the reserved section (which is all the way on the right of the theater, but still an excellent view).
The down side is you often have to eat really early. In January, we had to make 4:30 dinner reservations, and that was the latest they offered (Fantasmic started at 7:30pm that night). Not sure if you have to eat this early even if the show is at 9pm.
Still, this is the only way I'll do Fantasmic...it's a great show but I'd rather save 2 hours, do more rides, and have a decent meal.