As for the "science" of Superman and speculative fiction in general, it's helpful to have a firm sense of what the rules are and to solve problems within the context of said rules. Ideally, the rules should make for good and diverse kinds of story telling, especially for a world you're expecting the reader to live in for awhile. Even with comics that aren't really about speculative fiction, the humor is often against a backdrop of consistency and archetype.
You've essentially summarized my feelings on this particular issue here.
The important thing about science in science fiction - Superman and everywhere else - is not so much about being sticklers for plausible, real world physics, but
consistency with well defined rules. One example I like to use of this is Star Trek's Transporter device, which is not possible at least by how we understand physics today; thanks to Heisenberg's Uncertainty Principle, the very act of monitoring a particle (as would be required to to reassemble their atoms elsewhere) is not possible because the very act of observation shifts atoms' position. However, the Star Trek people are able to make us believe their teleporter works because it operates by rules they are consistent with and never violate: they cannot beam through forceshields, and as it is a drain on power, it can only be used at full energy, and so forth... Logically, there would be a backup in case such an all-important technology does not operate, so the Enterprise has shuttlecrafts - a credit to how well the writers of the show really thought all this through.
That said, this is no excuse for sloppy science. One writer of my acquaintance once called it the "Core of Mars is Made of Ice" slacking: in TOTAL RECALL, the fascinating premise of the movie, the idea that Mars might be made liveable by melting the poles, was totally sabotaged by an absurd declaration by Ahhh-nold: that the core of Mars is made of ice, which totally compromised any belief in the idea because it showed that the writer had really not done his homework.
Superman is a product of 1930s Futurism. I've argued on other occasions that Superman is by his nature a "period" character no matter what era his stories are set in. But more relevant to this discussion, I would say you can't remove Superman's science fiction angle.
One concern of mine is that a lot of writers have read nothing but comic books - not science texts, not science fiction, nothing, and so they have no experience in other things, which means they have nothing new to add. Look for instance, how well Kurt Busiek's knowledge of science fiction aided him in worldbuilding and grounding a society, as he did in his recent JLA arc, or how Alan Moore's knowledge of science introduced so many wonderful concepts in Supreme or Tom Strong.
Many people have told me the difference between Batman and Superman is that Superman's stories are light in tone, whereas Batman's are darker in tone. With respect to these fans, I don't agree with this. Batman was inspired by Zorro as well as the Shadow, and Bats does an awful lot of swashbuckling. Batman's world is more
stylized than truly dark, with giant typewriters and zeppelins, and gangsters in fedoras and pinstripe zoot suits. Batman's stories are escapist, like Tarzan's or the Lone Ranger's, and so by their very nature, they cannot be truly nihilistic. They are action stories with the underworld background to give it "color." The "dead of night" aspect of Batman's character gives him color just like Green Lantern's space opera angle gives that hero color. But Batman is not a noir hero any more than Green Lantern is a space opera hero.
Batman's stories could stand to be lighter in tone (Len Wein's Bat stories for instance, were wonderful, and Steve Englehart himself was much more playful than scary) and at the same time, Superman could stand to be darker, too. I mean "darker" in the sense of introducing intriguing science fiction concepts instead of tarnishing Superman's innate, immutable incorruptibility. Superman is science fiction, and science fiction gave us 1984 as well as SKYLARK OF SPACE; science fiction has creepy and weird ideas in its escapist stories.
For a related example, some role-playing games get caught up in such an elaborate, overcomplicated set of rules that players often find themselves more rule-playing rather than role-playing. The same thing applies to science and comics/S.F.
If a game is simple (like DC HEROES or PRINCE VALIANT), that's a strength. It should be noted that usually, "rules-light" games are based on a pair of simple ideas, and the games pass or fail depending on how well thought out these two or three ideas are. DC HEROES's comparison system and the concept of "APs" worked, whereas the White Wolf storyteller system failed, as its basic concept (the idea of dice pools) yielded wildly implausible and irregular results. On the other hand, there is something to be said for games with an extraordinary amount of detail. ROLEMASTER had a lot - a LOT - of rules, but it was consistent with all of them and they all fit together and balanced out. The trick is to make all the rules gel together instead of just tagging on new ones (which unfortunately, was what Palladium's approach was).
