That's a tough one. I am admittedly a non member. I am a member of only one club presently - the Buick Club of America. I have been a Walter P Chrysler Club member, a Peerless Club member as well as Olds and Cadillac LaSalle Club member.
One membership is not expensive but when you are a "generalist" like me, getting 4-5 $40 to $50 memberships due annually can cost money.
I am a forum hog. I get on the AACA forums daily and have left about 3300 posts in the last 4 years or so. My main contact with KF enthusiasts is through this forum and frankly, there is not much activity.
But when there is, especially when it is purely historical in nature, I love it. I am joining because of the forum and need to support a run at a 49 Virginian and hopefully a 49 Frazer. But at the same time I need to renew my BCA membership ($50) and want to join the AACA and Frazer Club so I will expend $200 in the next 4 weeks on all of these memberships. That doesn't even include a couple of other memberships I covet.