One other tidbit:
We did have one evening where we saw both the fireworks and the second showing of Fantasmic. It was actually quite easy.
We made a point of finding a spot near one of the ropes at the entrance to Frontierland. We got there around 9 PM, maybe just a tad later, and when the CMs came by asking for people to move forward, we did not, we made an aisle near us so people who wanted to join the crowd could easily get into the area.
From that vantage point, the fireworks were easy to see for the most part, except for some trees, and the angle was a bit silly, in that a lot of the fireworks are supposed to go off over and around the castle, but from our angle, they were off center. On the plus side, we could easily see Tink and Dumbo. (Last year we watched from over by Pixie Hollow and couldn't see them very easily because the castle got in the way most of the time.)
When the fireworks ended, we headed directly to Frontierland and near the steamboat / riverboat queue, they had a rope up so that people leaving the first Fantasmic could get out of there without the (now large) crowd interfering. Probably around 10:10 PM they walked us up into the area, and interestingly, most of the crowd dropped off super early, around the Golden Horseshoe. We kept walking up to the soundboard and light towers, and the area right in front of the soundboard is a "sitting only" area, dead center. The ushers wouldn't allow strollers to be left unfolded, or wheelchairs to be in the way, as anything above three feet or so would interfere with the soundboard operators being able to see everything.
This was a GREAT spot to watch Fantasmic... but if you needed to stand or had a wheelchair, you could have just kept going, closer to the launch for the Pirate Lair rafts, and had a great spot there, too, again, for whatever reason, the second show crowds all seemed to stop at that closest point to BTMRR or POTC and try to find seating there, as opposed to going further into New Orleans Square.
BTW, with that great vantage point for Fantasmic, I still think that show is probably the weakest of the major night shows... World of Color to me is the best, and I like the fireworks better than F! but they are pretty different.
(I have to make an effort some time to get down in front for WoC, we've had nice spots for the two times we've seen it, kind of dead center in the blue section, not too far back, no one directly in front of us, but it would be fun on a really hot day to be in the wet zone.)