Sometime, not too long ago, I seem to remember a discussion of the definition of spectral music running in the comment section. The latest issue of Skeptical Inquirer magazine includes an interview with composer Joshua Fineberg, who gives it a go:
We are creatures that are tremendously sensitive to timbre because the vowels of language depend on timbral perception, as does our auditory scene analysis. The fact that we are relatively less good at identifying things like pitches and intervals is part of why for a long time they were interesting.
Somebody give the poor man a hairdryer!