Definitely a fun episode.
And in fact, the idea of a holodeck on the original Enterprise (even for just a very brief time) may not even be that far-fetched: I read somewhere that Gene Roddenberry had originally suggested it for at least one of the TOS episodes but it ended up never materializing for both technical and budgetary reasons. However, a version of it
did appear in the TAS episode "The Practical Joker" (though it was called the "Recreation Room" there).
Also, this episode's holodeck character Sunny Lupino was no doubt an expy for Lucille Ball, whose Desilu Productions actually produced
Star Trek from its beginning before being sold to Gulf+Western (who had purchased Paramount Studios just a few short years earlier) partway through the show's run with Desilu then being renamed to Paramount Television. However, her name was likely an homage to Ida Lupino, who was the only woman to have directed an episode of the original
The Twilight Zone ("The Masks") and the only person on that show to have both directed an episode and starred on another ("The Sixteen-Millimeter Shrine").
-G