one of my great delights is to see and hear a top class singer, duo or band at the top of their game with a good sound system and excellent acoustics.

For me nothing beats hearing a top-class performer without any amplification at all. Ironically, this would be a lot harder if all those top-class performers were getting the audiences they deserve (and making a decent living).

Leveller: they are always well attended, to the extent that singers are usually restricted to 2, or sometimes 3, songs during the evening

Slight digression: one reason I'm going to my local singers' club less often these days is that it's too well attended - on both the last two occasions I've been down, everyone got one song. Don't know what the answer to that is, other than starting earlier - or waiting for the numbers to right themselves as people like me drift away ("nobody goes there any more, it's too busy").