I don't think having Padme in the Original Trilogy would have really "enhanced" things, especially in the first two films. In "A New Hope" and "Empire Strikes Back" we aren't supposed to sympathize with Vader, and are meant to see him as more of an inhuman and unfeeling monster. Having Padme in those films would ruin part of the menacing feeling we got from Vader when those movies first came out and he might not have been as effective as a villain as he was.
Hypothetically if she was in the original trilogy, there would have been no reason to give up Luke and Leia and they would have been raised by Vader and the Emperor. The entire story would have to have redone, with perhaps Luke rebelling against his father and turning away from the life of a sith.