I personally think that one/two/three day events would be a blast. Perhaps have a series of smaller events stretched over the weeks/months leading up to the "big game". Sort of an ongoing game, I think if people knew that they were part of an ongoing "conflict" and that they could get in on the final big "end game" and the smaller games could even be used to slowly work up to a multi day event, start with a couple 8 hour games, then a 12 hour game, then build to the 24 or 48 hour games.
Now don't get me wrong I can see that this would be a planning nightmare. But a series of games would give groups time to learn to work together, squads and teams would grow out of the continued series of play. That and someone that might not be able to attend the "big day" could still participate by playing in some of the lead up days. If a running total of points were kept it may encourage people to come out to make sure there "team" stayed in the lead or to help bring them from behind.
I know this is a bit of a ramble, but its late and my body wont sleep (my brain seems to be napping, but the body is awake).
Hope that this made some sort of sense.