Should Movies Update Classic Scifi, Or Go Retro?

There are two ways of taking a science fiction classic and bringing it to the screen: You can bring it up to date, setting it in the present day and revamping the characters accordingly, like Steven Spielberg's War Of The Worlds. Or you can set it in the era when it was written, and painstakingly recreate the time and place that gave birth to it, like Zack Snyder's Watchmen movie. Which route do you think works better for movies of classic novels?

Should Movies Update Classic Scifi, Or Go Retro?

Really, it's impossible to recapture the era when something originated completely. The past is a foreign country, and all that. And the older the work in question, the more stuff there's likely to be that a 21st century audience would find bizarre or offensive. The best you can hope for is a kind of retro-futurist look back at the golden age.

(I was inspired to think about this by yesterday's discussion of the rumored John Carter movie, and how many people were violently opposed to a WotW-style update.)

How likely is it that film-makers will be able to reconstruct the look of a bygone era and make us understand the real-world issues that the old stories were dealing with metaphorically? (Even Watchmen, which only takes place 23 years ago, is going to have a hard time hauling our asses back into a Cold War mindset.)

And there's another dimension to the issue of filming Golden Age science fiction: stories set in the future, like the Lensmen saga or The Moon Is A Harsh Mistress, both in development right now. Should movies of those books try to recapture a 1930s or 1960s vision of the future? How far should film-makers go in trying to pay a retro-futurist tribute to these classic works, maybe in a sort of Sky Captain and the World of Tomorrow style?

Instead of doing a poll, I'm just throwing the question out there. On one level, it's just a yes-or-no question: should film-makers try to be faithful to the eras when classic SF texts were written? On another level, it's a much more complex issue. What do you think?