Another fan theory on Superman I liked was by Al Shroeder, where he said that Superboy and Abin Sur probably met, and it may have been Abin Sur who taught Superboy how to navigate in space.
A lot of the things that people take for granted as being a product of the internet and the internet age have been around for a VERY, VERY long time. There are fanzines and Amateur Press Associations, for sure, but fanfiction is also very, very old...as old as the sixties and seventies, when they were mailed around in manilla envelopes.
Even erotic fanfiction has been around for a while. There's an apocryphal story that Shatner was shown a very early Kirk/Spock slash fiction story on the set of Star Trek's second season...and consequently went absolutely ape!
Similarly, the term "Mary Sue" is not a product of the internet age, but goes back to an especially legendarily horrible late sixties Star Trek fanzine.
I have another fan theory that I came up with a while back:
As we already know, the Guardians of the Universe had a plan to breed the ultimate Green Lantern - this plan would have reached fruition with the offspring of Jor-El and Lara. Here's the new part: Another element of the Guardians' plan was that this "super" GL would eventually become the leader of the Green Lantern Corps and bring it to new heights, ultimately taking on, and defeating, all threats to life and to civilization - specifically the growing threat of Darkseid's search for the Anti-Life equation.
Darkseid forsaw this fatal impedence to his power, so he destroyed Krypton in order the thwart the Guardians and prevent the success of their plan.
Interesting, but making Darkseid responsible for the destruction of Krypton seems totally wrong for the same reason that making anyone responsible for it (e.g. Black Zero) seems wrong: because the tragedy of it all was that it was senseless nature or the gods or fate, instead of being an act of malice and genocide.
Also, Darkseid is a schemer and a plotter. Something as unsubtle as blowing up a whole planet is within his power but just not his style.
But you are asking the right questions: because of all the factors you mention, to what extent did Darkseid take an interest in Krypton? Was he watching it? Was it possible he had contact with the planet, maybe even with someone like Jor-El? It would be interesting to know the answer. Even if Darkseid wasn't responsible for the destruction of Krypton, he would certainly take an interest in Kal-El as the sole survivor. It's very likely that Darkseid and Superman met a considerable amount of time before.
I never really knew how people found out about fan theories. Now, certainly, with the internet, but in the "old days" how did people know what other fans thought? Was this the kind of stuff that filled those old fanzines?
Don't forget letters columns. As Permanus pointed out, those things are fantastic because of how great they are in creating a sense of community. Some of the more interesting details are present in lettercols: for instance, the explanation for why Lana Lang never suspected Clark Kent was Superman because they jumped from Smallville to Metropolis. "Pete Ross moved from Smallville to Metropolis too. Does that make HIM Superman?" The editor responds. "Lots of small-town kids move to the big city."
(Similarly, I always hated those cruddy old 70s "documentaries" that suggested space aliens built the pyramids. Not because it's goofy "science," but because it insults the Egyptians. Frankly I'm more impressed by the notion they did it themselves).
Awww, c'mon! I always loved those spooky seventies shows like IN SEARCH OF... with Leonard Nimoy. In fact, I wanted to start an IN SEARCH OF... fansite a while back, though I thought better of it as I wasn't sure how to upload movie clips.
First, there was the ultra, ultra spooky synthesizer music, made all the more frightening because they usually synched it up to pictures of the Easter Island heads or whatever.
Then you had the way Leonard paused before important words and then repeated them. as in: "We begin now the search." (Dramatic Pause) "The search...for Bigfoot."
This is astonishingly easy to parody. As in, "Here we come to Fort Ross in California, where many a cap was popped into many an Indian. But was a cap ever popped in the behind...the behind of
Bigfoot?"
I also loved how Leonard Nimoy was never willing to really "rough it." The camera crews went over to the godforsaken armpits of the earth, but Nimoy was always somewhere comfortable in a jacket sipping brandy. The furthest he ever went in the series that I can recall was at a coffeehouse within sight of the pyramids.
I mean, how often did they do this: "The search...the search for Bigfoot has taken us here...here, to this four-star lodge..."
There have been other "Unsolved Mystery" shows, but it never got better than Spock trying to show how Greek temples in the Aegean from the air create a Maltese Cross or something.
One especially hilarious episode (at least in a black way with the 20/20 foresight of our globally warming world) was one where they tried to argue that soon, an Ice Age will rock mankind.
My favorite part of IN SEARCH OF... was how they vascillated between theories that are considered "out there" even by the terrifyingly low standards of crackpot historians (such as how they tried to argue that an alien black hole transponder is below the Bermuda Triangle, or how without the slightest trace of irony, they referred to the Tiahuanaco ruins as "Earth Base One"), to conservative historical pieces (they were talking about the Vikings in America for instance, back when this was a "fringe" theory).
My personal favorite episode was the one on Coral Castle, where supposedly a 4'11", crazy Latvian immigrant used his mind powers to create a palace to a dead girlfriend. I say favorite, because I worked at Coral Castle for a summer to make some pocket money.
My favorite part of the tour was where, on behalf of the park, we were supposed to emphasize to visitors that Ed was NOT a spy for the Axis powers. They deny it just enough that it became plausible.
As for PJ Farmer, I never really liked the way he kept tying together all the fictional characters of past, present and future in one huge family tree. To me, it dimishes the importance of the individual to suggest that some genetic destiny accounts for his or her greatness, and it belittles the human race as a whole to limit all greatness to one or two bloodlines. It turns fictional heroes into a sort of aristocracy, which is anathema to my American upbringing and actually runs counter to the raison d'etre of many of the characters involved.
I don't necessarily have a problem with all these characters being related, but PJF had a tendency to replace one straightforward idea with a complicated theory that negates his original premise. He started off TARZAN ALIVE by saying he was going to treat Tarzan as having really happened, and says that some of his feats of strength must surely have been exaggerations by his author. Okay, I can buy that.
But then he goes into an explanation that because Tarzan wasn't massive, he must have mutated muscles. Wha - ?
If I do have any misgivings about the PJF explanations, it is that it points out how ruthlessly Anglo-Saxon Protestant the entire heroic community is. This is true without PJF having to point it out, but if you can have everybody be related it brings the point home further.
I remember an old collection of fan articles on Star Trek that explained pretty neatly how Spock could have been born, despite the fact that a red-blooded mother could never carry a green-blooded fetus to term. It was kind of disappointing to see that work unused when they showed a normal birth in "Star Trek 5." Then again, a lot of things in that film were disappointing...
Well, Spock's "natural birth" in that scene doesn't necessarily mean he wasn't laboratory created and then placed in his mother's womb to develop.
The original TREK fan magazine, pre-Next Generation, was one really great source of speculative essays. My all-time favorite was one where they speculated what sort of home planet the tribbles must have.
One that was in the PJF mold was where they speculated Doc Savage might be a Vulcan. Doc Savage had strength that dwarfed even that of very strong men; his hearing was beyond human range (which is not entirely possible to attribute to exercises), he used a variation of the Vulcan Neck Pinch, he was very logical and never showed strong emotion ever, and never showed strong interest in women. There are moments (see THE CZAR OF FEAR, among others) where Doc did something very much like the Vulcan Mind Meld: he gets information by a criminal by gripping the crook's face (!) and then asking questions. Doc, like Spock, has weird powers over women (see "The Omega Glory").