Reader question - When are remakes justified?

A Twitter-submitted question from @Swiss_Fox:

When do you think a remake is appropriate? What conditions/qualities need to be present/met in the original? In the remake?

My personal feeling is that there are few good reasons to remake a good movie. Would anything be gained by remaking Star Wars? ET? Back to the Future? If the original is already timeless, remaking it is a losing game.

In the case where the original film was based on other source material, then there might be room for reinterpretation - particularly in cases where the original adaptation took some liberties with the source material. Thus, I could see someone justifying a remake of To Kill a Mockingbird... but would it be wise to remake Gone With the Wind? I've long thought that you could get an interesting movie out of re-adapting The Wizard of Oz so that it's more faithful to the book. However, the problem there is that the original is SO iconic that the filmmakers would probably be facing an uphill battle.

I think there's more justification for remaking a film that might have had an interesting idea, but unsuccessful execution the first time around. If there's something new to be said with the material - a different tone, a reexamination of how the old themes play in a new, modern context - it also gives more justification for the remake.

Most of the time, though, the studio finds remakes attractive because they're pre-sold... so remaking a bomb would run counter to that desire. Having said that, I'd love to remake I Know What You Did Last Summer the way it was meant to be.

Just my opinion. How do you guys feel?