The trick for Fantasmic is to see it at the later (10:30) show on nights when they show it twice, which is usually. It's MUCH less crowded then.
Get to the area about 9:20, while the first show is still going on. Hang back around HM or Riverbelle. At 9:25, the first show ends and the fireworks begin. Some people will leave, though most will stay for the fireworks. You'll be able to find a spot that would only be OK for F!, but is just fine for watching fireworks. Watch the fireworks along with the other folks. When the fireworks end, almost everyone will get up and leave. You should be able to find an excellent spot to see F! at that time.
DW & I used this procedure on 9/27. Got front row sitting-only spots to see F!.
ETA - The fireworks are much better from in front of the castle. So you still need to plan a separate evening for seeing them from that location. I just meant that, if you're seeing them from around ROA anyway, you should be able to find a spot that's OK for that.
HTH,
Bob