Okay, done.
It works fine using v.9.1.230 (this morning's build).
I did it twice:
First, I imported (via right-click context in Windows Explorer) an old .m3u playlist which listed about 15 WMA9-loseless files. Since I recently removed all my WMA files from the library (and went back to ape), MC not only added the playlist but imported the files as well.
Seeing the error of my ways, I deleted the imported playlist and removed the imported WMA files. I then imported the same playlist, only this time with the correct APE files specified. This time, it imported the playlist, but didn't bother importing any files (since they were already in my library).
In both cases, a new branch entitled "Imported Playlists" showed up under the "Playlists" branch after I clicked "OK," and the playlist's filename (minus the .m3u extension of course) showed up as a child of this new branch.
Omni