The food and price are exactly the same.....however if you book it specifically as a "Fantasmic Dinner Package" then when you pay you will be given passes to sit in a specific area of the theatre. It is the two sections all the way to stage right (meaning if you're on stage facing the audience it's to your right). You are advised to arrive 30-45 minutes before the show as at about 30 minutes before they will open those sections to general seating.
Somewhere, there is a thread with a wonderful map that Robo made....hopefully he'll see this and post it, or I'll try to find it to link.
Personally.....IF you are already planning to eat at that restaurant, then I'd go ahead. Otherwise.....I personally would prefer to sit more centered, and have never had to arrive more than 30 minutes early to do so (I do NOT go during the summer or during a holiday week, so those times you may need to go much much earlier). So, you're not going to save time......and in my opinion those aren't the best seats in the house (though there are no "bad" seats I'm told since the show does sort of move around to all areas).
If you're buying the meal solely because you think you're getting something special by doing so....save your money, lol.