Danny,
I find this entire forum hugely useful - not just for all the great advice, but also for being able recognise bad advice, weigh up different opininons, etc. I am currently training for my ATPL, alongside a full time job, and often use these resources for help, and soemtimers just a distraction or a bit of light relief!
My view (obviously!) would be that just holding a professional licence should be sufficient - after all, if one of the main reasons is for discussing CHIRP, then that is exactly the kind of stuff low houred pilots-in-waiting should be reading up on.
Perhaps it's time to introduce a small handling fee for members to cover the admin to receive and validate an application? Most other forums that I am a member of have a "premium" area where a small fee gets much wider access.
DW.hether open or hidden - maybe hidden will give the opportunity for an area specifically for professionals to be able to discuss things in privacy - something that clearly many people want given the number of non-specialist members currently viewing and posting.
Only my tuppence worth.
DW.