With a '64 Airstream Bambi II you would qualify for membership in either or both groups.
As I understand it, CAC is intended for those interested in the classic shaped (non-wide-body, non-painted, non-fiberglass) "silver" trailers/MoHos of any age whereas the VAC is intended for any model of Airstream that is 25 years or older - painted or not.
If your interest is more oriented towards the "care & feeding of vintage rigs" you would find the VAC more suitable. If you are more into the iconic "classic" imagery of Airstreams and not as much of the nostalgia or restoration, then the CAC may better suit your style. Some people are members of both...