The LD copy only has 400 lines of resolution, minus the letterboxing black. You can't magically make more lines of resolution out of that. Making an anamorphic disc from that would look worse. It's like reencoding a 128kbps MP3 to a 256kbps MP3 in hopes that it will sound better.

Doing some math, it seems that the 2.35:1 aspect ratio of the Star Wars movies letterboxed to fit in 4:3 leaves about 227 lines of resolution for the actual movie. If it were produced anamorphically (16:9), it would result in 302 lines of resolution. That's a loss of 25%. If it were an anamorphic DVD (assuming a native resolution for DVDs of 540 lines), it would be 408 lines. That's a loss of about 44%.