"perhaps young people who are interested in folk (and yes, there are a fair few about) aren't all that interested in folk clubs"

True. I sense a wave of something on the tails of performers like Rachel Unthank which may well fill festivals and gigs but not folk clubs.

"Can the health of the folk club really still be held up as a yardstick for the health of the tradition?"

No. Just as some Stones fans ended up on a trail that lead to Muddy Waters and Robert Johnson, a few Winterset kids might finish up at Bert Lloyd but folk clubs will have to meet them half way which is probably not what folk clubs are about. My collection is large and growing and I last went in a folk club in 1975.