Girtablulu after adding the workplace switcher did you reboot
I said I'd try it on my dev machine this morning, and now I've done that. The Plasma SSD was still in the machine from my attempts yesterday, so I can't be sure of what steps might have been done before, although all past attempts had been unsuccessful, but I do know it's been rebooted at least once recently.
This morning, I opened the desktop settings, created 8 virtual desktops, and pressed the Accept button. Just ONE group of 8 desktops was created, and now I'm thinking even more seriously about adopting the Plasma edition for daily use on that computer.
It would hurt too much to give up my beloved Budgie altogether, though. I'm going to keep it going in a VM on my laptop for playing games.
EDIT: I'm not sure of the exact steps needed, or the exact order to perform them, but apparently a reboot is needed as part of the process. Just as you suggested yesterday. Thanks again!