I think the lightsabers looked awful in the 2004 versions because of the changes in contrast and color timing; the picture was darkened overall. This had the unfortunate side effect of darkening the white cores of the sabers. The color timing screw-up was also responsible for making Luke’s lightsaber look green on the Falcon.
They only redid some of the lightsabers in the 2004 OT, including much of the Ben/Vader duel. But after people complained enough, they finally went and fixed some of the 2004 problems for the 2011 release. Although, even then, they didn’t fix everything, as evident by the faded saber cores in the Bespin duel.