All writers do it. Inside jokes and appreciative nods. In my last book, my wife inspired the name for a grand airship. The scientific theory explaining the root of the tale is named for two of my favourite classic SF authors. One of the businesses on a bustling street is apparently owned by a good friend (or his alternate Earth counterpart).
But, musing off the top of my melon here, when do "nods" become some flavour of "plagiarism"? I recently heard tell of an author that named a planet "Trantor", supposedly as a nod to Isaac Asimov and his "Foundation" works. My first kneejerk reaction was "nice". Then I began to wonder. Naming a planet after a famous planet has a whiff of someone attempting to bask in reflected glory. Even if the moment is "lampshaded" between the characters, referencing Asimov and explaining the name choice, it still feels a case can be made of the author glomming a little free street cred from the SF Grand Master.
Is that what I did when I cited the "Laumer-Leinster Theory"? It wasn't my overt intention.
Or am I making far too big a pile of rocks from a few pebbles?
Another aspect of sly references and nods is whether they are plot-crucial or not. Well, they certainly should not be crucial. Nobody had to be familiar with the works of either Leinster or Laumer to understand the flow of my book. I hope this other author wasn't so crass as to expect every reader to immediately recognize "Trantor" and therefore be able to appreciate subsequent plot points.
I recently read a pile of skunk vomit disguised as a book. My great guilt is that I finished the thing.** This author does nothing but reference other works; songs, movies, books, games. A paragraph does not go by without such a mention. I guess these weren't "nods", per se. This guy hung his entire story on the reader being as savvy as himself for 1980's (predominantly) pop culture. Damn, it was bad writing.
I reckon, whether it's a clever inside joke or wholesale borrowing, as long as the oblivious reader's experience isn't diminished, then the reference is probably A-OK. A baseline of enjoyment has to be maintained. Every reader should hopefully get an "A" experience. The reader who gets the nods and winks has an A+ ride.
**I won't go into names and titles, to keep the discussion on track. Someday I may start reviewing books here. Then names will be named.