I disagree with the majority. I believe that the entire OT should be redone with fresh new, CG effects. Spiffing up the duels and battles, replacing puppets with pixels, fixing up outdated looking computer systems (such as the death star computers in IV), fixing the sabers once and for all, and adding in some scenes of Palpatine and the Imperial Senate on Coruscant... these changes would make the OT way better.
Adding Vader and Palpatine on Coruscant would also be cool-- if they could find a good place to add this into one of the movies (most likely IV). I think Coruscant adds to the breadth and scope of the films... it makes SW seem very epic and huge.
Anyways, I believe that GL will one day spiff up the OT to match the PT... When watching the final edition of the OT, you won't even be able to tell the difference between the two trilogies (Effects wise)... it will be as if the PT and OT were made in the same generation... in order of I-VI.
For a sample of what can be done to spiff up the OT, just watch all of the menus on the OT DVD's... they look great. The best one is on the bonus disc where Luke is practicing with his saber on board the Falcon (from IV)... it looks so cleaned up and perfect! Really awesome.