It's a rare singer in my not so humble opinion (IMNSHO) who can carry an evening of unaccompanied singing. Roy Harris is one, as are Helen Schneyer, Jean Redpath and Lou Killen. In gospel, The Fairfield Four and Doyle Lawson and Quicksilver(0n the many songs they do unaccompanied) are so full and rich that you don't even think about adding instruments.

As for people who sing in an "egotesticle fog", I'm, not sure an instrument would help..

Jerry