I don't get how anyone can say that there is a difference between things that are "useful" and those that aren't. Everything is useful. A Monet painting conveys a sense of peace and pleasure to the person who buys it. Or, it makes him feel good about himself because he's rich enough to afford it.
I can't think of a single thing that a single human being has every bought in the history of mankind that wasn't useful. Everything is useful to someone.