"In the pursuit of music reproduction in the home it is my firm belief that you must listen to live music every now & again so that you know & understand how real music,with real instruments,in real physical spaces sounds..."
Although I've only been into audio for the past twenty years or so, I've been playing guitar (both acoustic and electric) steadily since the mid-seventies. Not once has it ever ocurred to me to utilize the sound of a guitar "in a real physical space" as a benchmark for my audio system.
As a player, I'm acutely aware that there are potentially millions of different "real" instrument sounds. Ask twenty players to play the same instrument and you will get twenty different "real" sounds. Same thing goes with "real physical spaces"-- play the same guitar in twenty different settings and odds are, you'll hear a lot of variation. So who determines the benchmark, when there are so many potential possibilities?