Regarding the MSA, increasing participation is tied to increasing visibility. It's not unlike selling something in the APUG Classifieds. The items that sell best are those that garner the most visibility.
As it seems to work now, somebody creates a theme. Then two months of time pass without any real public discussion. Few posts. No questions. No creative insights. No technical information. Nothing. Then after two months, somebody creates a new theme.
I think what's needed is for the participants to start talking about what they're doing, as they do it.
Are you posting a new photo? How about including an accompanying post about how that photo came to be? What motivated you? And why? What did you have to do to accomplish that photo? What obstacles did you have to overcome? What worked? What didn't? What might you do differently next time? What were your thought processes?
And given the nature of APUG, adding some technical details couldn't hurt either. Camera? Film? Equipment? Techniques?
And if you are reading someone else's descriptions, comment on them. Explain how you once faced similar motivations. Or obstacles. Or used similar equipment. Or chose different equipment. Or different techniques. How did you manage to pull it off? Or how did you fail?
What this approach would do is the same thing it does in the Classifieds. Repeatedly bump the current MSA thread to the top. That's where people look when they first log on to read. Interesting threads generate the most... interest.
And beyond that, you'll all learn a little bit more about each other. And maybe rethink some of your approaches to photography. And maybe even make some new online friends in the process.
As it stand right now, the MSA thread is at the top of the queue only a couple days out of every 60. That's why nobody knows much about it.