As an audience member I don't care [what I believe our transatlantic cousins call diddleysquat] what a performer is wearing. Acker Bilk and some of the other UK jazz bands wore "uniforms" for tv and concert halls but leather jackets and t-shirts etc for clubs, and usually played their best in the latter. Whe I saw PP&M at Birmingham town hall many, many years ago I was taken aback to see them in "Penguin suits"/evening gown. The Clanceys' roll-neck sweaters were instantly recognisable, the Corries and the Spinners had uniform but casual shirts, but this is probably the need to market an image to a wider audience. Sonny and Brownie wore dungarees both times I was lucky enough to see them. I would have hated to see them forced into penguin suits (which they probably had to in some venues).
Sorry, I'm rambling again.
RtS ( who's never worn a "penguin suit" and gets away with it even at [rare]formal "dos", and no longer wears a suit to work (come to think about it, no longer owns a suit!)