Some audience members CAN hear the difference between guitars, and it makes a difference to them. In any event, at times it behooves the performer to educate the audience by exposing them to the sounds. As for the Variax...it depends on how convincing you want your sound to be...and it certainly doesn't convince me. Also, sometimes other band members are to be considered. For example, the concertina player in my duo much prefers the sound of one guitar over others, and a singer I used to play with would often say she preferred one guitar over others depending on the song. Having played a lot of acoustic house concerts I can honestly say that in the right circumstances switching up guitars can be appreciated by the audience.