I have no means of assessing the meaning of the ebb and flow of posts, because the Agora is the only forum in which I participate.
That said, it seems only natural that there will be periods of greater and lesser postings. People come to these forums for a variety of reasons, and other reasons take them away.
The Agora, started just six months ago, has just suffered its first stumble, and perhaps a stumble of this sort is natural and maybe even necessary. The volume of posts had risen, as others have noted, to a level where it was all but impossible to keep up with them. Too, the Agora has some 500 or even more members. What if they all participated heavily? How could anyone keep up? Being of less interest to me than other language areas, I had already pretty much abandoned the Grammar forum and posted less than I would have wished to the Suggest a Word forum.
Maybe the Agora would be a better place with fewer posts, but posts of a higher quality. That’s a proposition that’s hugely subjective, of course, but perhaps it bears consideration.
That leads me to the matter of "off-topic." I think it’s healthy and desirable for threads to meander, and I believe that some of the most interesting threads were the ones that, well, meandered and then meandered some more and never even came back to the original topic. I have, however, been put off by the volume of posts that I can only describe as idle chatter, with little or no edifying content. Hard to define? You bet. But I’d also bet that most of us knew them when we saw them.
In sum, this is our community, and the merit of its content can only reflect the effort we put into it.
Oh, yes: I still want to win the Loto so I can buy me an electronic OED. ;)