Without its stylized, minimalist sets and surreal atmosphere, “Spectre of the Gun” would have been just another mediocre Earthlike-planet-on-the-Forty-Acres-backlot episode.
I once read a really interesting Australian newspaper journalist's review of an 80s repeat of "The Empath", never a particular favourite of mine - but the review made me appreciate it. The reviewer noted that the episode wasn't as dated as many others, due to being mostly filmed on a darkened, empty sound stage. Also, I'd only ever seen damaged prints before, and this version showed me the two tortured, dead scientists in their transparent display tubes. Very disturbing/effective.
In 1980, as I slowly caught up on all the eps I'd missed, I happened upon the movie "Barbarella", at my ST club's Christmas party. I decided that John Phillip Law (Pygar, the blind angel) would have been perfect
as a feisty Andorian crewmember to join TOS's third or fourth season. Imagine my surprise, decades
later, when plans were afoot to add Shran to Archer's crew had it gone to a fifth season.
I also would have loved to have seen Alan Dean Foster's double episode for the fourth season of TOS, featuring Kirk's Klingon exchange student former-roommate from the Academy. ADF eventually used this idea to pad out "Star Trek Log Seven" (TAS adaptations) to a novel-length story.