You are right, I went for simplification there.
The reason why the edges still look correct there is that all metal parts are of type 1,
and do not model the metal by quads plus edges.
Doing the latter would create wrong colors for the edges.
That glitch is what I wanted to avoid for the 9V parts.
I just grepped all the 9V files of the PT, and in fact, they don't have such an error.
So I retract my argument above. Coloring of edges currently is not wrong,
so no correction is needed by separating into metal/plastic.
The reason why the edges still look correct there is that all metal parts are of type 1,
and do not model the metal by quads plus edges.
Doing the latter would create wrong colors for the edges.
That glitch is what I wanted to avoid for the 9V parts.
I just grepped all the 9V files of the PT, and in fact, they don't have such an error.
So I retract my argument above. Coloring of edges currently is not wrong,
so no correction is needed by separating into metal/plastic.