In terms of New Hollywood, the typical stuff comes to mind (French Connection, Godfathers, Dog Day Afternoon, Dear Hunter, Serpico, Chinatown, Bonnie & Clyde, Butch Cassidy and Sundance Kid). Many very countercultural, with an anti-establishment streak to them.

I do think that yeah, you can't suddenly make the prequels overtly gritty and reminiscent of that era, given that the originals were such fun escapist space fantasy. However, I do believe there is a way to have aspects of that kind of an element subtly present and working symbolically.

Say for example if in the second film, Obi-Wan and Anakin are separated for much of the story, that's where one could really do some interesting stuff with tone.

Kenobi's settings feel reminiscent of the Golden Age of Hollywood and thus, the Republic: Bright, with vast colors, large settings, and an outworldly, yet personally pleasing style. Some visual hints that its starting to decay and fall apart a bit, yet it still retains a classical feel. People always seem to be part of crowds and groups. Even Kenobi's clean and quasi-majestic Jedi attire seems right at home.

Skywalker's story feels much differently. Muted color palette, confined settings, even a harsher feel in editing with the cuts. Various characters are much more isolated and alone. Anakin looks more haggard, his Jedi clothes not really fitting, with bits of dirt and grime starting to appear on his attire. He sticks out much more in his settings, never seems entirely relaxed. Have just enough little visual clues to make the surroundings feel bit too familiar and close to home for the audience.

Again, the key thing is subtlety and doing in a way that isn't overt and taking the audience out of the films. No doubt its a hell of gamble because its so easy to mess up. But if it can be pulled off, it would make for really interesting trilogy.