I just realised I wrote this reply but never sent it! Oops
Can you pinpoint why you have less of an issue with Google+?
I think it’s the fact that meetup emails a lot about related groups, and pushes you to join and RSVP. There’s a big shiny red button in your inbox with no tangible commitment attached to it, so people are encouraged to push it.
I think when you have to seek out the meetup (or see a tweet/post etc) and say you're attending, it carries much more weight than just acknowledging the suggestion. Google+ understands that the individual events are part of a broader community but doesn't necessarily push you to join a following one. I don't like it that much, and it's not a significant improvement over meetup in terms of features, but it at least has that going for it.
What is it that you would do that might help to improve this.
That's still unclear, and the features & purpose of what I want to build aren't really fleshed out yet. I was thinking of something that helps with the extra stuff as well as "ticketing" for events. So logging IRC channels, helping with automated tweets reminding about the event, mailing lists and so on. In terms of the features I'd use for Brum.js it's ticketing, tweets, website and possibly mailing list.
If anyone has suggestions I'd love to hear them!