And speaking of not knowing whether I'm missing something or Simplify3D is, here's where I got with the dual extruder skirt problem:
First, I was getting only the left extruder printing a skirt, and I could not get the right extruder to generate a skirt no matter what I did to the setup.
I contacted Simplify3D support, and finally got the answer that I needed for each of the left and right processes to define the other extruder (and. . . why, exactly? And why does that result in only the left extruder printing a skirt? Seems so freaking arbritrary, not to mention arcane).
So I plugged in the modified processes, and I discover that it prints the skirt INTERLEAVED right, left, right, left. But get this---it's PRINTED in that order: left extruder prints a skirt perimeter. Right extruder prints a skirt perimeter. Left extruder prints another skirt perimeter. And so forth. And after the right extruder prints the last skirt perimeter, then the left extruder starts printing the first layer, followed by the right extruder printing its first layer.
If you think about that, you'll realize that it completely undermines the whole purpose of having a skirt in the first place.
Typically the skirt is used to get the filament flowing, because when the extruder sits still for too long, it takes some time to get it going, and that problem is worst when attempting to print the first layer on the bed surface. Hence the need to print the skirt to give a good long time for the filament to get going, then immediately move to the first layer.
Simplify3D's way of doing a dual extrusion skirt means that each nozzle gets primed multiple times, for no particular reason, and that both of them have a significant delay between priming on the skirt and printing the part, which is just wrong, wrong, wrong.
It kind of makes me wonder if the guys who do the programming at Simplify3D have every actually used a 3D printer. . .
Sorry, it has been frustrating working with Simplify3D support, and I had to get that rant off my chest.