Hmm. It seems that no one has found the 50 folder limit to be a problem when building their WMP library.
For anyone interested, I solved this problem by moving my music and audio books to a top level folders, one for music and another for audio books. Now all I have to add to WMP are these two top level folders. It seems there isn't much of a problem with WMP marching through sub folders and adding all my music and audio books. It's also a little easier for me to manage my media files.
Thanks for viewing this thread.
RoseM