I feel the turnover is somewhat due to the fact that most (or at least many) of the "old guys" have completed their builds and have moved on to driving them, have sold their Cobras, etc. Combine that demographic with the economically-induced drop off in new kit sales, which translates into less being built at any one time, and, presto, you have falling Club Cobra participation.
There are a few of us long timers who still rely on this site as the best resource for Cobra info, advice, and general entertainment. I haven't met many offline, but I don't think I could have solved some of the issues I came across so far during my build without you guys. I'm still building mine and you bast*%#$ are driving yours!