they arent cleaning up laser blasts for the complete preservationist version. they are correcting the colors (of the entire film) to match what the colors were when it was shown in theaters (it seems they have some good information as to the true color of the scenes).
the only things they are 'fixing' is the things that were messed up when the movie was put onto the laser disc and underwent the thx remastering.
then, from there, they will have their own project if they desire where they fix matte lines, or lightsabers.
at least, thats my understanding, correct me if im wrong.
preservation has nothing to do with Lucas' 'original vision' it has to do what he originally showed. If it was the former than lucas could call his 2004 edits preservation which they are clearly not. Preservation preserves the 'warts and all' so that the film is shown just as they were able to get it when they showed it, it keeps the 'mistakes/errors' that were caused by the limitations of the technology of that time.
-Darth Simon