I might also suggest A Canticle For Leibowitz by Miller. An exploration of the human soul and theology through a post-Armageddon world.
I don't know; I'm not the one who "own about 4500 scifi books and have read 2-3 times that so I have a good knowledge base to draw on".
C J Cherryh. Anything by her. Specifically her Alliance-Union universe stuff and her Foreigner stuff. Her Alliance-Union stories have the gritty realism feel/vibe that the first 2 Alien movies have. She's not heavy on the science but it's not unrealistic. Moreso, her stories are all about the character interaction, sociological and political aspects and, maybe, even moral ramifications. She struggles a little, in my opinion, with action sequences though and it seems that the really big action moments tend to happen "off camera." I love Neal Stephenson's works. Again, his stuff seems realistic yet he doesn't get bogged down with overly technical details. While Ben Bova's "Grand Tour" books are pretty realistic "hard" SciFi, his Sam Gunn series, set in the same universe, is nothing but rip-roaring fun. Brian Daley was another author that seemed to have the "fun factor" nailed. Too bad his life was cut short.
Viewing these themes in a first contact setting you can try Mary Doria Russell 's The Sparrow and its sequel Childern of God. I also recommend China Miéville's Perdido Street Station. A combination of steampunk and fantasy that I found weirdly compelling.