I walked out of Sci-Fi the one time I went there, because the service was so bad.
If you must go, why not just get some ice creem or a shake and some fries?
If you must sit down to eat at MGM, Mama Melrose is pretty good. I personally would have lunch at the ABC Commissary and have the sit-down meal somewhere at the World Showcase at Epcot.
Chefs de France is my favorite, but if you also want entertainment, how about the Biergarten? Something else pretty special could be PS's at the Rose and Crown around an hour and a half before Illuminations. If you ask to sit on the patio, you will be able to enjoy dessert and coffee just as Illuminations is starting!
And I agree with others, Rainforest Cafes are everywhere. I would go someplace that I can't go everywhere else. At DD, how about Wolfgang Puck's Express (or whatever it is called - the counter service one)? It'll be better food and cheaper prices! If you must do that "theme dining" kind of thing, isn't there a Planet Hollywood at DD?
Sorry, I know you spent a lot of time trying to make these choices, and we are all changing them on you! It must be very frustrating. But really, if I were to just have one or two sit-down meals at the World, it absolutley wouldn't be Sci-Fi!
Good luck, and let us know what you decide!
Nicole