I suppose it depends how much of the act is chat, and how much songs or tunes.
We heard Ali Bain & Phil Cunningham last night, quite an experience. As Severn says of the Dillards it sounded spontaneous.
But some of the anecdotes were quite long, so the first time they certainly add to the evening, if they come round again next year (I missed them last year) I would not remember how many of the tunes were the same and would like to hear them again if I recognised them. But the same jokes would be something to sit through.