The vast majority of people, given Superman's powers, would be supervillains; or, at least, super zeroes. Those that would not simply take everything they wanted would at best contract out their powers for monetary gain - maybe having a conscience about what they get paid to do, maybe not. Superman not only uses his powers to save lives, he does so with anonymity; he does it explicitly for nothing but doing good, with no return for himself. Sure, people sing praises for Superman, but no one adulates Clark Kent, who receives - and asks - no compensation for his work as Superman.
Sure, his story might not lend itself to constant telling over a span of eighty years - what story would? This is why I don't read comics. But as modern myth, Superman inspires and encourages us all to be better people, in a way no other superhero has. Myths live in the retelling; if Superman is "reinvented" every now and then, to start a retelling, this should be viewed as a good thing. By resetting the myth and starting it over again with new trappings to reflect a more modern world, the myth is reborn to inspire once again. So long as the essence of that myth remains true, it remains the same whatever trappings attached to it. Superman has remained essentially the same character throughout his retellings.
That's where Batman failed, and why I'm not really a fan of Batman. Sure, Frank Miller rebirthed the myth of Batman to a new generation, but in doing so, he changed the essence of Batman, changing him from a man steeped in superstition because of the power it had over weak-minded thugs to a gritty bad-ass barely better than a weak-minded thug himself. At least most animated depictions of Batman have retained that core goodness underneath his crusty demeanour; of late, cinematic and literary portrayals of Batman have betrayed the myth laying underneath, and created a generation without the inspiration Superman gave an earlier one.