"Did the popularity of the folk club begin to fizzle out with the dawning of the more insular singaround?" Other way round, I'd say. When the numbers go down for other reasons and it's down to a faithful few, it tends to turn into a singaround. And the pub gets rid of the function room, but is all right about allowing singing in the bar.

Performance poets typically use the book as a prop, and there are some singers who do that as well. As with Bob Copper. (Or Henry Kipper.) And that's maybe the answer - if you use a songbook, make use of it for more than just the words, it's potentially a way of punctuating and pointing a song.