Online media's size limitations . . . a challenge

Bigger is not always better.  This statement is relevant to a trend I've noticed with online discussion groups.  At some point, (I venture about 200 to 500 members) the group risks losing the magical formula and relevance of a smaller community.  Then, the choice is heavy moderation and control -- or the degradation of the group into a useless collection of self-serving junk postings and advertisements.

I've seen this in the Design and Construction Network's LinkedIn group, now with more than 37,000 members.  Some years ago, in much earlier stages, you could read some really interesting discussions.  Now . . . well, the site is full of cross-posted crap from employment agencies scouring for candidates, and junk promotional messages.

I don't fault the group or its organizers.  Voluntary moderators could spend hours clearing out the junk and, well, the junk reappears.  As the group grows in size, the cohesion and specific relevance to its participants declines.  In essence, it becomes something of a very large ghost town.

The Construction Marketing Ideas LinkedIn group is experiencing these challenges.  I visit once or sometimes twice a day for a bit of housecleaning, clearing out the self-serving garbage and hopefully encouraging useful discussions.  These are, alas, relatively few and far between.

Probably the group would benefit from some proactive moderation and leadership, encouraging discussion, debate, and active networking.  But I have a day job, too.  How would you handle the situation?