Resetting the winfilecache didn't change anything.
I then disabled the greater majority of my installed extensions, leaving only those from Webassist and PVII.
At this point, I'm happy to report that I can edit any menu.
Before I disabled the other extensions, I could create a "new" menu and edit it with no problem. When that editing window opened, it also listed the other two menus included in the powerstore2 installation. I could edit the first powerstore menu listed, but clicking on the second menu brought up the "toJSONString" loop, and I was done.
So, bottom line, evidence points to another extension, and if I ever have a half a day to do nothing but open and close dreamweaver and the extension manager, then I'll do the research. If you are curious about the list of now disabled extensions, I can list them for you. As to how the "toJSONString" problem is triggered, I have no clue. You're the coder, not me.
I really appreciate your input.