I think this would be the best solution. To compress the information further, it would also be good if the sidebar block only showed meetups yet to happen, and all others relegated to a "past meetups" link. As of today, April 11, it might look like (but with nice fonts and everything):
Meetups
Edinburgh LW Meetup Saturday April 16th
Ottawa LW Meetup Saturday April 16th
past meetups
That would need some automatic way of discerning what the date of a meetup is.
IMO, there's a distinction between regular meetups, and one-shot meetups. It wouldn't make sense for a newcomer to see only one-shot meetups on the list, when a community in their city already exists.
Perhaps some sort of calendar would make sense, where anyone can post one-shot meetups, and regular meetups are represented by a recurring event.
I've been browsing LessWrong less often as of late, and I believe that one of the reasons is because I don't want to get all excited all over a new insightful LW post, only to discover that it's a meetup in a city that I'm not even in.
And for newbies to the site in particular, they're not going to see all the awesomeness of this site if they simply look at the frontpage and think it's a community just for meetups.
I'm sure meetup discussions can go somewhere prominent. Maybe a separate section can be devoted to them.