So what's the threshold at which point someone's own individual intellectual property is culturally important enough to become the property of society as a whole?
Life of the Author + 70 years or 120 years. Look, I'm not advocating that we actually seize the copyrights or enjoin him from further derivative works, but I think griping about the pillaging of our communal childhoods is well within the bounds of public discourse. Nothing will be added by making it 3D, and if that includes redoing all of the miniature work in CGI then what is the point? It was an amazing bit of space opera with groundbreaking special effects (and notably, a much better plot than Avatar. Not That That Is Hard.), and things tend to get worse when you try to improve the original work. Look at the butcherings of Shakespeare that the Victorians did. The point is that he shouldn't, and that every time he tries it gets worse.
There's only one real counter example, which is Blade Runner, for which the latter Director's cut was a vast improvement from the print run (which the studio butchered). I'd even argue that the Final cut is better than the Director's cut. But Ridley Scott was just finally pulling his version of the film from the footage, not adding unnecessary footage. (He didn't have full control over the Director's Cut, and let's face it, he's a much better director than Lucas.)