The simpilest and quickest sollution is to add some action. Only problem with that is if not done propperly it could get a burst of activity and then drop off again. Course when I say action it wouldn't have to be say one of the major factions that is not attending the expo launching a full out assault. it could be say a demonstration going wrong somehow, a more subtle attack like a bombing
Of course it could also be something less dire like say an announcement across the whole expo about a particular demonstration thats about to start, say a new prototype someone brought along is being put through its paces.
I assume you have something like the above more dangerous type actiions planned to bring us all together and make us a group rather than just people who have for hte most part just met, just depends on how soon do you want it to happen, now to pick up activity, or hold a little to get some more character exposition out.