So the parade/fireworks viewing is one of the topics I've been meaning to give additional thoughts on. Of any of the details I wrote about this is the one area I have a feeling could end up being different for everyone. This is purely me speculating and reacting to what I saw. Part of me was even hesitant to post about our experience in case this particular component turned out to change. I never did see this as an official amenity on any published material, only Twitter/blog chatter.
The reserved viewing areas are only so big and there are other people/groups that have access to them. When Disney let me know about the holiday parade, they used the term "we were able to secure four spots for you." The fact that at first it was not available and then was gave me the impression the Tomorrowland cabana managers were having to coordinate (if not negotiate) with other parts of the park and other demand generators of reserved spots, which surely is the case. There are countless groups - be it paid VIPs or other special interest groups - that I'm sure Disney is trying to accommodate for things like this on a daily basis.
We were the only ones in a cabana on our day. If all four were filled with 8 people each, there is no way 32 people could even fit in the small reserved spot we had for the holiday parade in addition to the other people that were there. While I'm assuming Disney could have come up with another location for such a circumstance, I don't know that for a fact.
Until we see more first hand experiences I'd probably recomend to keep an open mind about the parade/fireworks viewings, or at least stay flexible just in case.
(Not that you asked, but if it were me, I'd go to two parties over the cabana. Obviously a lot of factors involved, but that's my gut reaction.)