I'm once again indulging myself in a rationally indefensible fondness, but it makes me happy and harms no one so why not?

You could look at it a different way: The whole point of being rational is to get a better outcome, not just to be rational per se. And we typically use emotion to decide whether that outcome really is better or not.

So, in this sense, art is a not just a thing, but also a service that makes you feel a certain way. (See also: light is both a particle and a wave.)

This art, in your particular case, is rendering good service.