We originally had the dessert party reserved for Labor Day but cancelled due to Dorian and moved our
MNSSHP to last Friday 8/30. I wrote that my original plan was to watch the second parade, but we changed it to the first parade and watched near CBJ and as soon as the last float passed, we cut through the path to Adventureland, quick bathroom break and got to the HUB by the time the Incredibles floats were near the castle. That said.... I would almost think that if you got a spot in the HUB for the first parade, even if it wasn't front row, you would be in a much better position for the fireworks. As soon as the parade rounded near the castle people did flood the area, from both behind the parade (which I why I DONT recommend following the parade along the route, unless you were close to the last float) and from Adventureland. And my party wasn't super crowded because of Dorian.
If you watched the first parade from the HUB you could stay there for the fireworks and then watch the second parade again from a better location. It eats up some time, but that area does get crowded. If you did the dessert party, that would also eat up some time as well, just for comparison. When the parade finished everyone from Main St. started coming up as well.
The only thing I would also add is that once Jack came on stage people who couldn't see him kept trying to move and budge in for a better look. They do announce that they don't want people moving around in the low light once the show starts, but people don't listen. Aside from the hedges and things blocking some of the view, Jack himself is not that easy to see unless you are close enough or have an unobstructed view.
You could also ask a CM about the garden in front of Casey's. There was a private event in there the night we were there, but I don't think that's always the case and sometimes it's open. ????