As a newcomer to this group, but certainly not a newcomer to the internet or Usenet, I have seen newsgroups "attacked" before, sometimes for years, but, I have seen some recover.
As an avid runner, I saw rec.running go from a very informative group, to one with 70% garbage within 6 months. It stayed this way for 1 1/2 years or so, but now it's almost crap free. I'll have to admit, some had more of a backbone than I, and they stuck it out, posting their relevant information regardless of all the junk that was in there.
Eventually, the kiddies grew bored and moved on, however, it took while. You just have to ignore them and keep on plugging. 1 1/2 years seems like a long time, and it is, but eventually it will get better.
Above all, though, you *must* ignore them.