I have heard it said on a number of occasions that 1/f spectra are very commonly encountered among natural signals, and one might perhaps expect the auditory system to reflect this fact in its design (perhaps the fact that auditory filters get wider at higher CF and are approximately logarithmically spaced is a simple relfection of the 1/f nature of many sounds?)
There's a bit of work on how the auditory system might have adapted to such filters given the structure of sound. It doesn't have an obvious connection to 1/f spectra, but it comes up with a pretty good reason as to why auditory filters are the way they are. My work is more CS oriented: http://web.media.mit.edu/~paris/phd/paris-pre.pdf Lewicki's work has more neuro-credibility, mentions 1/f in passing: http://www-2.cs.cmu.edu/~lewicki/papers/Lewicki-NatNeurosci-02.pdf Paris