Well, I went 13. Finally finished the project tonight, or at least most of the way. Still need to bump/install 13 on the server machine here and the Office PC, but I can get that done tomorrow (and the Server box hardly ever actually uses MC). I noticed one issue with the Customize View dialog while working on the library reconfig, though...
If you uncheck "Allow Tree Selection" in Customize View on a View that is not one of the main top-level Views (not Audio, Video, or Images), you lose the ability to collapse the view by clicking on it's Disclosure Triangle. The View always stays "open" from then on, unless you close and re-open it's parent View. This makes sense for the Top-Level schemes because you can't really collapse them and still use them.
However, in my new Library setup, I have a couple of Views that act sort of like "folders" for other sets of Views (Imports, for example, which has a bunch of child Views that show my recent imports in different ways) but which are themselves children of the top-level schemes. So, my Audio View has an Imports child, which contains a whole set of Imports-related Views. It'd be nice to set the Imports child-view to not allow tree selection, but I still want to be able to Collapse that view when I'm not using it.