This has been the subject of some debate in the past, both on and off the group. An analysis by Colin Rosenstiel showed 405 different posters in cam.misc and 140 in cam.transport over a three month period in late 1997 (although that did include some duplicates). What sort of lurker to poster ratio there is we can argue over forever, but even a modest ratio would suggest over 1000 readers.
It must also be admitted that many of those 405 posters were single posts whereas the most enthusiastic posters clocked up around 90 posts each in that period.
More recently Chris Lightfoot ran a weekly traffic analysis on cam.misc and cam.transport, which will give you an idea of who is posting and about what in July 2004.
Mark Carroll used to look after a cam.* regulars Web page, but it went away for a while (long story) so, when the wiki appeared it seemed sensible to instead have people look after their own cam.regulars entries.