I am a huge Bernard Herrmann fan and I am appalled at how often his music is used but uncredited (The Artist, etc.) especially when it's not a work in public domain. One of my favorites is The Octopus from the soundtrack to Beneath the 12-Mile Reef BMG/RCA Victor 0707-2-RG. Everything he did was stellar.
But even I must admit that even the soundtrack from Vertigo (arguably his best work) could not exist without the legacy of Wagner's Tristan und Isolde and Rachmaninoff's Isle of the Dead (1909) and Symphony No. 2 (1906-07), and Ravel's Daphnis Et Chloé -And that trickles down to every film composer who can now also lean a little on Ligeti and Górecki. I have yet to hear film music that does not have some Classical or Romantic DNA in it. -Unless it's one of those sine wave drone soundtracks. And I find that to be a cop-out.
Just like Fred Steiner so wisely seized upon Ravel's Daphnis Et Chloé: 2. Entrance of Daphnis and Chloe and 11. Invocation to Pan by the Nymphs and the Prayer of Daphnis for his work on Star Trek. Great stuff that worked with the genre.
Basically, John Williams owes debts directly Rachmaninoff, Vaughan Williams, Ravel, and Holst. All sci-fi film composers have been touched by Holst. And all of this debt to Holst would not have been possible without Rachmaninoff's 2-minute Intermezzo from the opera Aleko that was written in 1892; and the absolute gold standard of Dies irae expanded to it's maximum possible effect in Isle of the Dead which was written in 1909.
It's pretty much impossible not to have something sound like something else. I suppose the trick is in not being so blatant or overly-seduved by the sheer beauty of what the greats have left us. This is something I struggle against.
We have all inherited such a treasure of great music and it is my hope that we will draw on the beautiful to write the new.
OP: Thank you for this lively discussion.