There's nothing wrong with going back and fixing a film so it's more faithful to the filmmaker's original vision. Look at Touch of Evil or the recently restored Metropolis. Of course, the effects thing can be tricky. What if while adding the rediscovered lost footage to Metropolis the Murnau Foundation also decided to update the sci-fi classic with some extra aircraft here, a little tweaking of the robot's transformation there? Maybe it's revealed that Fritz Lang originally had wanted random ronto creatures walking around the city, so they put those in, some in comic relief situations.
The latest campaign for a film to be bettered with an effects-improving special edition is Star Trek V: The Final Frontier. TrekWeb is behind the mission, directed at Paramount and CBS, as well as the film's director and star, William Shatner, whose blessing they hope to receive. Apparently the main issue is with the poor quality of effects employed for the sequel, which is currently thought to be one of the worst installments in the franchise, and with the deletion of certain scenes intended to be a part of the climax which were excised due to their especially inadequate visuals.
They quote screenwriter David Loughery, who admits to being disappointed with the "shoddy and ludicrous" execution of the effects-dependent scenes he wrote, and cite the successful campaigns for the new versions of Superman II and Star Trek: The Motion Picture as favored examples of the Special Edition craze. If you're a Trekkie who'd like to see a remastered and restored director's cut of Star Trek V, TrekWeb has listed addresses and phone numbers to contact in order to share your support and desire for a Special Edition.
If that's successful, what film would you like to see campaigned for next? No need to name movies that are "improving" effects-wise by being remade, like Logan's Run. Or those whose bad effects have become guilty pleasures, like Troll 2 and anything by Ed Wood. But there are certainly a lot of movies, even many made in the past decade, that would have been better had their effects been better. Would Howard the Duck be improved if the duck suit is replaced with a CG Howard? Should all movies with CG werewolves be revisited by better artists and released in box set form (including An American Werewolf in Paris, Cursed, Harry Potter and the Prisoner of Azkaban, Twilight: New Moon, Van Helsing, etc. etc. etc.)?
What else would you choose?