John,

Rather than turn the group into fully moderated, how about screening
membership? That is, set up the archives so anyone can read them, but
those who want to post must join, and the join is screened. That way,
should someone have enough energy to jump through the hoops to become
member, then they're likely to become a contribution (or at least not
mess in our nest). And, of course, if they do mess in the nest, they
can be removed with relative ease.

-Keith