There have been comics writers who have tried for a fair amount of scientific plausibility to justify or ameliorate the fanciful things in comics universes. Chris Claremont and John Byrne did a lot of that in X-Men, e.g. having Nightcrawler's teleports obey conservation of momentum. Byrne tried to make Superman's powers relatively more plausible in his 1986 reboot, and he worked with hard-SF writer Larry Niven to develop a more scientifically grounded series bible for Green Lantern, IIRC, whose ideas were used in their graphic novel Green Lantern: Ganthet's Tale. (The bit I remember most was when Hal accelerated away from his target at relativistic speed so that the green light from his ring would be redshifted into yellow.)
People tend to think of scientific plausibility as an inhibition for writing fiction, but I feel it's the opposite -- knowing how science works can give you a lot more ideas that would never have occurred to you otherwise.
Depends on the genre and the story you're trying to tell. Nothing wrong with scientifically rigorous hard-sf, but it's not the only possible approach to SF, fantasy, horror, or larger-than-life superheroic, comic-book adventures. And I resist the idea that such fanciful notions are something that need to be "justified" or "ameliorated" where comic-book stories are concerned.
To my mind, they're a feature, not a bug.
Personally, I can't say that I ever thought that "scientific plausibility" was what appealed to me about comics books and superheroes. It was more about about the sheer fun and coolness of, say, a guy flying through space on a cosmic surfboard, an entire bottle city of miniaturized Kryptonians, a super-powered ghost growing to the size of a solar system and hurling planets and moons around, a talking tiger in a bow tie, Red Kryptonite turning Superman into a giant insect-man, Norse gods fighting giant alien robots in the middle of Manhattan, a daredevil motorcyclist with a flaming skull for a head, and, yes, an entire Legion of Super-Pets, complete with capes.
(Says the guy who still can't believe I got paid to novelize a fight between Wonder Woman and Frankenstein's monster. Thank you, Grant Morrison.)