And even in my older age-group, I can think of some who, having learned an instrument, spend every bit of spare time at sessions but rarely attend any clubs or “spectator sport”.

That would be me. I've been playing folk music since the mid-60s and never felt folk clubs had much to do with it. The age group of the people I've played with has widened over the decades but the lower end hasn't shifted that much. I'd have had a very different impression if I'd frequented institutions where people thought real ale had anything to with music or that possession of a brand-name guitar with a cool model number would make it more memorable.