Do many State affiliates of NAGC have a Homeschooling Chapter? Ours does not. Rather our State affiliate is operated primarily as a tool to involve parents to advocate for the public school teachers and their unions legislatively; the focus is on parental push for more money to be allocated.
"Voluntary membership" groups vary considerably from year to year. In general individuals make a few friends, acquaintances, or contacts and socialize/associate with them apart from the group, having less interest in newcomers as time goes by.
Because groups compete fiercely for grants then create services of benefit to "all", a focus on the needs of the gifted may be lost.