Yes you can watch the fireworks and listen to the music from either California Grill (with reservation and if open), TOTWL or your room (with the right view) regardless of night and if there's a party.
The music will be the right music for whatever the fireworks show is.
Even if you don't have MK view, you still get the channel that has the music, so you could just listen to Wishes or whatever on your TV without watching the fireworks.
Hallowishes is the best of the 3 (Wishes,
MVMCP or
MNSSHP). The Christmas fireworks probably the worst.