Mulan2,
Looks like you are enjoying your Boardwalk membership. Welcome Home.
The last poster is most likely correct. We won't know until next week for sure when BLT opens, but it looks like that a room key will be needed to access the sky bridge to get to the tower.
I also attended the Member event a few weeks ago, and as good as the viewing of the Magic Kingdom fireworks are from The Top of the World Lounge and observation deck, the view from the sky bridge is better. The perspective of the fireworks and the castle work so much better from the bridge.
Enjoy your stay.
Robert