If you aren’t a hotel guest with a room facing the park, your options are very limited.
If you are a club level guest, you can watch from the club lounge on the 12th floor.
The only way to get to the roof (without entering off limits to guests areas) is to dine at California Grill that day. You don’t need to be dining at the restaurant at the time of the show, but you do need to have eaten there that day. If you did, they will let you back upstairs to watch.
They also have a large bar in California Grill, but I really don’t know what the rules are if you don’t have a dining reservation.
The deck on the north side of the 4th floor is directly under the monorail beams and your view will be obstructed, either partly or completely depending on where you are able to stand. I also believe they do not pipe the soundtrack to this deck. The only place where there are speakers relaying the soundtrack are in California Grill or out on the north observation deck.
As for Bay Lake Tower, you have to be a registered guest or the guest of a registered guest (and I’m sure you have to be accompanied by the guest, but I couldn’t swear to it).