I hear accordion and piano, shofar and violin, marimba, vibes and miscellaneous percussion, and I think: Alvin Curran. I hear car horns and metronomes, and I think: Ligeti. I hear a basic Pierrot ensemble plus clinking glassware, BBs, bird calls and rustling tree branch and I think: John Zorn (ahem, his "classical" music, anyway). I fixate on the instrumentation, and am impressed or bored by the way the instruments are written for or played, and sort of...forget...to evaluate the music for theme or structure, motive or development. Zorn, Ligeti, and Curran are masters in many ways beyond orchestration, of course; there are others, however, who seem content to just stop at color, stop at the orchestration, and let the surprise of an "unusual" instrument seduce our ears and distract us from structure and form (or lack of it).
Concerts of new music tend to be cleverly programmed with orchestration foremost in mind. A guitar quartet might show, visually, some superficial relationship to a string quartet on the same program but, because strings are rubbed, amplified, grated, or left to feedback, actually pays homage to the meandering electronic track in another piece. The string quartet, meanwhile, full of strong pizzicatos or tappings of the bow on the instrument's body, might seem companion to creative percussion writing elsewhere on the program, especially when that involves bowing cymbals and striking woodblocks with fingertips. It's color, color, everywhere!
If you asked every composer in a given school's graduate program (and I'll be the first to admit that our Ravels and Stravinskys are probably not lurking in the halls of some graduate program) to write a dozen piano pieces, or a "symphonic movement" for thirty-two strings and timpani, and then you sat and blindly listened to all those pieces, would you be able to hear distinct voices? (I imagine you'd hear a fair share of derivative voices: ghosts.) If prevented from assembling a select and unique instrumentation, is a composer still able to assert a personal voice? How does one differentiate oneself if the parameters are reduced? How is it that I can distinguish Mendelssohn from Schumann when they speak through the same medium, when it's just the piano that I hear? How is it that sometimes I take meaning from what people have to say--their words, sentences, and whole ideas--and sometimes I can only hear the expression of their pitch, timbre or inflection?