Two notes:

During a performance in a local Chapters bookstore my wife wandered around to gauge the sound level and balance. She said there were a substantial number of people sitting just out of sight in the shelves, apparently content to enjoy what we were playing without becoming part of an "audience".

As to the taboo on applause during classical performance there is a famous recording of E. Power Biggs playing Bach in a infectious rhythm. The audience started to clap along vigorously and in time. It is exhilarating to listen to.

Michael