One of the greatest, intangible, benefits of membership in such 'clubs' is the credibility they endow on us as a group.
On your own, you are the nutball down the road who owns a 'tank'/'jeep'/'big ugly noisy rust bucket that scares the neighbours' (pick the most suitable discription). As a group, we are regarded as main stream antique vehicle collectors who have a preference for olive drab and dog turd brown.
Insurance companies are more willing to include our strange looking vehicles on their lists of low risk antiques, we enjoy the synergy of having a voice for antique vehicles in political circles; for example, it wasn't a lone dog that convinced the Province of Ontario to have historic vehicle plates and more recently, to allow the registration of 'year of manufacture' plates... it was the collective voice of the clubs.
Along with the benefits ably listed by RobDab, I consider the intangibles well worth the cost of a round of beer for my buds!
ends!
Cheers! Mike