(2) OMG -- you've never seen Westworld? And, of course, the ULTIMATE sci-fi western! Accept no substitutes.
As for Cat People: Wow... Is that worth a thread? Watch it and decide. I'd keep it separate since nobody appreciates the references in Inglorious Basterds, and they're muddled with The Crow, anyway.
Also remember that Firefly was aired out of order. So what thin story-arc was there didn't make sense, nor did the carefully crafted character development.
That's what I think killed it, in combination with the time slot/advertising.
The western itself has faded, yes. Though the themes are the same. The "journeyman" sci-fi format -- still alive and well, thanks to BSG -- is something westerns created. (And look at Caprica as the rancher format -- Bonanza, etc.) Sci-fi has aped westerns into the modern day (get ready for that feel with our small town cop hero in Walking Dead).
But as far as the western genre itself dying out... I think there's still room for a last gasp. Deadwood, as one example. Though to do it right in the modern day, you do need to combine it with something. The sci-fi western, the Shakespearean western...
Vietnam movies are a different ball of wax. Those represent a nation trying to heal. Notice how claims that the 91 Gulf War (something often said by media, Bush, and others) undid the wounds of Vietnam. There were lots of claims that the "victory" in 91 reversed our fortunes, etc. You then see a decline in Vietnam movies.
More obviously, we've been fighting what is soon going to become a generational war since 1991. Our war movies are now focused on that war.
American war movies, generally, have followed a pattern. During WWII, you get propaganda movies (Shores of Tripoli, Bataan, Destination Tokyo, etc. etc). After WWII, you get movies that focus more on personal issues (as far as the 50's and 60's could get away with) such as Attack, Iron Cross, The Caine Mutiny, Young Lions, etc.).
By the 70's, in an attempt to avoid Vietnam, WW2 films sort of reach the end of their thread. We're reduced to comedy and/or action. Dirty Dozen, Where Eagles Dare, Kelly's Heroes, etc.
Vietnam films were being pitched in the 60's and Hollywood, famously, refused to make them and shut every project down. Until... The later 70's. They just couldn't hold back the tide. The healing process begins with Deer Hunter, Taxi Driver, Coming Home, Apocalypse Now... All with a self-defensive fantastical element. The 80's sees the boom of "authentic" Vietnam movies -- Full Metal Jacket, Platoon, etc.
The Vietnam movie era dwindles in the early 90's (Heaven on Earth the last truly passable film, 1992). We get a brief resurgence of Spielberg history, and then we shift into our current war -- which is where we stand today. That, also, has seen movement from propaganda to defensive fantasy to social commentary.
