Your theory of consonance is in line with current theories about harmony. However, in our equally tempered system all intervals are actually slightly dissonant. This is because in true temperament, a song in C is very consonant, but because the fractions don't line up perfectly, the same song in F# is unlistenable because the intervals that sound nice in C are now dissonant. All music we hear is an approximation of consonance, but the differences are so minute that we barely notice it. Music is a lot more complex than this though, dissonance isn't a bad thing per say, in fact, interplay between consonant and dissonant harmonies has been an integral part of music for centuries now. Think of a diminished triad built on the major 7th resolving back to the root, this is a trademark example of a dissonant chord creating tension, after which it releases this tension through going back to the root.
You mentioned imitative music as an example of humanities preference for symmetry in music, humans like repitition when it comes to music, and I think it has more to do with that rather than symmetry. This is more because we like things that we already know, if something is extremely different from our current tastes, but still symmetrical, we won't like it. Try getting your grandma to listen to Cannibal Corpse and you'll see my point. This also explains why forms of music such as cantus firmus (basing a song on another song that already exists) have been so successful throughout the years.
I do agree that symmetry is often used in musical pieces, but whether I don't know whether that is because of symmetry, or familiarity.
Just my two cents haha, I hope you understand all of the terminology I used, if not I can totally explain.