I have bee using a set of Bosch 3-electrode plugs in my 1.9 WB (Bosch Super plug W8DTC).  These plug are not platinum.  They seem to work OK, no problems and no miracles.  They way the advantage of these plugs was explained to me was that as the electrode that was the easiest gap for the spark to jump wore down the spark would switch to the next electrode.  The spark could also move depending on mixture density and other thing that most of us could not understand.
George
'85 Westfalia