The comic book speculator market isn't normally the kind of cash cow that the 90s thought it was going to be. Unless you've got one of those very rare early superhero origin comics—or you happen to sell something random like Avengers #257 at the exact right time for a convenient movie tie-in—you're typically lucky to make even a dollar on an old comic.
Space Adventures #7 has nothing to do with superheroes, or non-superhero movie adaptations. But it's still coveted, probably because it contains a pre-Comics Code story called "Transformation" that was illustrated by Dick Giordano, who went on to become the Executive Editor at DC Comics, and written by a curiously uncredited author.
What's more interesting about the comic, however, is that it deals unexpectedly with transgender issues.
Here's a basic synopsis of the 8-page story from Comic Book Plus:
Anticipating nuclear war that would leave Earth barren of life, Lars Kranston convinces his colleagues to go to Mars. His paramour Betty Stone insists that she go as well. The ship crashes on Mars. Everyone but Lars and Betty are killed, but Lars thinks she died too. Betty wakes up suffering total amnesia. Lars decides to use the supplies that survived the wreck. He manages a complete sex change. The tumultuous situation on Earth dies down. The predicted war never occurs. Betty remembers the journey. She runs Lars, who explains his sex change to a woman. Betty breaks down at the revelation.
The representation of trans issues in the comic isn't quite perfect—after all, it was published just 2 years after Christine Jorgensen became the first widely-known trans person in America. Thematically, the comic deals more with an overly-simplistic binary understanding of "masculinity" and "femininity." I might even argue that it's more of a commentary on what we now talk about as "toxic masculinity"—the hyper-aggressive, unemotional, dangerously "logic"-obsessed stoic warmonger-types—than actual issues of body or gender dysphoria.
Still, it's an interesting piece of comics history.
To be fair, Charlton Comics in general has a very strange story; a friend of mine has been working on a documentary about the company for years, and has still barely scratched the surface. The company was originally founded in a small town outside of New Haven, by an Italian immigrant bricklayer who had spent time in prison for printing books of song lyrics that infringed on copyright laws. The company eventually began publishing a wide variety of comic book titles, from Westerns to horror comics to licensed comics about Flash Gordon and the Hanna-Barbera pantheon. They're also responsible for creating superhero characters such as Blue Beetle, Captain Atom, The Peacemaker, The Question, and Nightshade—all of whom were eventually bought by DC Comics, and used as the basis for the characters in Watchmen before being folded into the larger DC Universe.
And somewhere, in the course of all of that, they managed to publish an early sci-fi exploration of gender transformations.
You can read the full "Transformation" story from Space Adventures #7 here.