This is a good topic for discussion; thanks for bringing it up! I think each of us creates "original" music in the sense that we as composers create works of music that are uniquely our own. True, they may resemble certain styles and forms of other composers—I'm not sure one can ever escape that since all of our musical ideas are built upon stuff we've heard before and internalized. As we become more experienced, we're able to remove ourselves farther away from those influences, so our music slowly takes on its own voice.
As to the "style" of originality as defined by the classical music elites, I'm stumped there. The style of music heralded by the elites as "purely original" is, as you mentioned, atonal. Proponents of atonal music posit that it's a musical era just like Romantic or Impressionism, but I disagree; up until the Modern/Postmodern era of classical music, composers followed the natural "rules" of music. Debussy (an Impressionist for those following along at home) did some weird things with tonality but he obeyed the rules. The human ear is wired to interpret certain pitch relationships as consonant and others as dissonant—and these days, some as purely chaotic. Modern/postmodern classical music, with its strong atonality, is the first musical movement to actually rebel against this natural rule, or at least disregard it, in the hopes of staying original.
So, all this to say that modern composers have abandoned tonality because they believe there's nothing "original" left to be had there. Again, I disagree. It takes a lot more work and creative thinking to find an original voice in the world of tonality, but it's entirely possible—and very satisfying! I've a hunch that the great composers of our generation remembered 100 years down the road will not be the progressive, 12-tone serialists churning out mind-boggling, gut-wrenching cacophonies; rather, it will be those who continued to tinker with tonality and made music that meshed with the human soul.
My goals are rather simple: write music that I like. I'd much prefer to revolutionize music than reach a big audience, but (for reasons mentioned above) I don't feel like that's going in the direction of the current avant-garde styles. There's still hundreds of years' worth of exploring to do in the world of tonality!
So how original do we need to be? Well, be as original as you want to be! Some people create amazing works that sound like Beethoven or Mozart could have written. Others' sound like something from an outfit from Mars. The problem I find is that composers are either cliché tonal composers (little musical training) or else they're atonal. This probably has to do with the fact that atonal music is the prima donna right now among the elites; atonal music will receive the most praise (and it's difficult to criticize since it doesn't follow a lot of rules), so "serious" composers seek originality via that route.
If there are atonal composers reading this, please don't get the wrong impression! I respect your compositional styles 100%; my point is that atonal music is not the sole arbiter of originality.
As you might have guessed, my music is strongly tonal. However, I use a rich combination of chords throughout so it doesn't sound too cliché. In fact, I hate having to use conventional chord progressions; I strive to avoid them when I can. My works have a strong thematic element to them but are rarely melody-driven (in other words, not like Tchaikovsky and other Romantics). I also use a lot of unconventional modulations that loosely tie to the previous key. And I love counterpoint—I always try to use it when I can. It helps ensure that all players have "interesting" parts to play!
I guess I'm describing Impressionism, and maybe that category best fits my musical style. Anyone is welcome to take a listen to some of my stuff and give their own opinion. 🙂