I vote to stay Simplex, but...
I had the original Prestige (plastic) version DR's on my GP when I got it last year. The rear DR had a shipping incident, which caused a couple of broken pulley teeth. Other than that...it shifted fine.
During my resto on the bike, I decided to up-grade the DR's to Simplex Super LJ components and LOVE them for precise shifting and lack of major (potentially troublesome) plastic components.

And who could argue with the better
looking LJ's?
http://velo-orange.blogspot.com/2006...erailleur.html