I can understand if some of the "mathy" types of people that populate this site have a perception that topics relating to art and music are "fluffy" and unprestigious, but what I've never been able to understand is why this perception doesn't seem to get updated once they run into people who are similarly "mathy" but also interested in art and music.

This may be a perception that some people have, but I've always perceived music as a) very mathematical, and b) not at all unprestigious. In the high school I went to, people who were smart academically and also talented in music were much higher-status than people who were only involved in academic subjects. (I'm not saying this is a universal perception, or even a good perception to have, but it's what I've observed.)