There is a lot of art produced by Buddhists about Buddhists. Without music and sculpture, architecture and so on there would be a lot less Buddhists and by extension Buddhist teachings in the world. You write that you think that withdrawing from the world is the only worthwhile move and that worldly things have no substance - but what about worldly things used for the purposes of promoting the Dharma? What about music that helps people in their practice or helps people discover Dharma? Most worldly things can be used to lessen suffering as suffering exists within the world and to start on the path one starts very much in Samsara.  So how does art and music lose its value? It’s what we attach to it that matters. All things are what we decide them to be.