I read the complete short stories of Arthur C. Clarke recently and one of the things that really struck me was that several of the early stories (long before NASA) had lunar-native plants growing wild on the Moon. For a hard SF writer I found that extraordinary; you forget just how much the speculative consensus has changed within quite a short period.
In a similar vein, several of the early stories seem convinced by the evidence for psionics...
Clarke had a pretty interesting progression from belief in many paranormal claims to hard core skeptic over his lifetime, and similarly from pantheist to atheist.
Before the advent of cell phones it seemed expedient to have telepathy for quick communication --- that said, Heinlein did predict them in his novel _Space Cadet_ (though they don't make more than a brief appearance).
In a similar vein, several of the early stories seem convinced by the evidence for psionics...