I never thought I would say this, but I'm now in favor of George Lucas re-doing the original movies. If you watch the original versions, they just can't hold a candle to the new movies. If you watch them in sequence, there's a massive drop in quality and special effects around Episode IV. The new scenes and effects in the Special Edition DVDs do a lot to improve them.
In fact, I think they need to do more, especially to IV: A New Hope. Specifically, I wish they would re-do the battle between Darth vader and Obi-Wan Kenobi. When I was a kid, it was dazzling, but try watching it again. By any standard, especially compared to the new lightsaber battles in the series, it's terrible. They just bang their lightsabers at each other really slowly, and Obi-Wan spins around once for no reason. That's about it. Considering this is the culmination of their rivalry over decades, it's very anti-climactic. It has to be longer with better fighting. They could re-shoot the scene using doubles and the face-replacement technology they used for Count Dooku. That would be awesome.
They could also stand to re-shoot the X-Wing battle with the Death Star. In the current version, the ships just move from left to right across the screen. That wouldn't be hard at all. Just re-create it with pure CGI and have them zipping around, doing twists and stunts like in the opening of Episode III. I'm sure he's already working on it.