My understanding of the club rego system was that you needed to be a financial member of the car club who offers the club rego. Depending on the clubs constitution you may have to attend a certain number of club run events a year to qualify access to that clubs club rego system but that will vary from club to club. If your membership expires then your access to the club rego system would lapse soon after. No different to being a RSL club member and access to the various services and facilities offered by the RSL.
You are right about the decreasing number of car clubs. That is not restricted to the regional areas but I think the decline may be more rapid than there city based associates. I have been a member of a number of sporting car clubs over the years and they all struggle for numbers for these days. The advent of the internet and various online social groups makes it so much easier to communicate with like minded enthusiasts. When I first started out a lot of the information and stories came from attending the monthly club meetings and reading the newsletter that arrived in the mail. Now you can read updates on Facebook from various competitors as the events progress.

Anthony