In the vast realm of speculative fiction, there exist a number of blends of science fiction and fantasy. "Magical space opera" is term I haven't heard used before, but a relative of mine in the know says isn't original to me. But perhaps what I mean by the term isn't standard and can inspire some stories of a new type.
To get to what I mean, let's define space opera. Wikipedia has it as: "A subgenre of science fiction that often emphasizes romantic, often melodramatic adventure, set mainly or entirely in outer space, usually involving conflict between opponents possessing advanced technologies and abilities. The term has no relation to music but is analogous to 'soap opera'."
A lot people think of classic science fiction stories when they think of space opera (an example I'd give is Ray Gun Revival, which deliberately tried to revive the style of Golden Age science fiction space opera). But really, as opposed to hard science fiction (which is scientifically accurate) or other subgenres like planetary romance, sword and planet, or military science fiction, most of the science fiction we see in movies is really space opera. Neither Star Wars nor Star Trek are truly realistic scientifically, are set in space, tend to be melodramatic, and have emphasized conflict between technically advanced foes. This is also true in a different way of movies like Armageddon and Independence Day, which certainly aren't hard science fiction but don't entirely qualify as military or anything else--but they do emphasize romantic and melodramatic elements. It's actually harder to find a sci-fi movie that isn't space opera in one way or other than to find one that is.
What I would do with "magical" space opera is create stories virtually identical to space opera stories, except with the twist of typical fantasy elements, including magic, featured in the story to replace things space opera employs as technological. So a starship powered by warp drive would have a "dilithium stone" instead of "dilithium crystals" as the heart of the energy system. Technology like a video monitor would still exist, but would be powered my magical creatures like pixies. Gnomes, elves, and goblins could be part of outer space crews.
Really my idea relates back to my earlier blog post A World of Magic-Powered Technology, in which I postulated a society that mirrored our in most ways, but magic backed the technology instead of being powered by electrical and chemical motors. If this world so nearly like the twenty-first century in so many ways, but with a base in magic, advanced to the point it developed space travel, that world would have stories that I'd call "magical space opera."
To see better what I mean, check out this for-pay story of mine on Amazon: A Little Problem with the Dilithium Stone.