How's this for stradling the fence.....
Fantasmic ONLY if you have a Fantasmic Dinner Package. Fantasmic seating seems to fill up at least an hour before the show (and then they close the line) and what are you going to do with those kids sitting on a bench for an hour??? If you have the dinner package, you can go in a separate entrance with seating saved for you with no line. If you go this route, book the dinner early.
As for Spectromagic, if you know where to go, you can get a good spot to see it up untill a few minutes before the parade. Also, how can you beat the Magic Kingdom at night?