I thoroughly agree. Math is beautiful, or can be, and we should encourage its use for beauty!

Regarding the metaphysics of art, Plotinus has you covered. The arts that imitate what we experience in nature (say, painting or sculpting) are physical; the arts that generalize from nature to produce un-natural things (say, music, or to your point, math as an art) are spiritual (in his schema, belong to the level of souls, just like gods and angels and so on); finally, the arts that draw on a general theory to practical ends (say, medicine or engineering) are in the middle.