It's kind of a dilemma.
Yes, the Fantasmic dinner package "saves" you some seats. However, in order to get some really good seats, you have to enter almost as early as the regular folks. It's not like you can get there 5 minutes to showtime and have prime seats. In other words, even the saved seats tend to fill up quickly, you just have a seat saved for you.
The dinner packages are nice; however, I probably wouldn't do it again because the seat I had wasn't really that much better than one I could have gotten myself.
The walk down the "special" entrance is quite long too.