Another solution I've found is: right-click playlist, click "Edit Playlist in Action Window". Like the two instances solution, this gives two playlists simultaneously.
Disadvantages:
* the Action Window is quite small and I've not found a way to enlarge or relocate it.
* For keyboard users, switching is more awkward - TAB from main file list to Action Window goes out of its way to visit Search. The whole round trip is ragged so perhaps this will get fixed up.
* There are some anomalous interactions e.g. in Action Window playlist select one instance of a repeated track, then above main window playlist click Shuffle - AW selection changes to include all instances of the repeated track.
Advantages:
* simplicity
Hoping this thread gets Matt's imagination going since playlist management has never been 100% elegant.
Playlist use presents many different requirements, but for mine, MC it the best of the various music librarians I've tried. If Matt does have time for playlist functionality, I hope he'll improve the simple widely-applicable stuff like the navigation (see original question), rather than very specialist features such as your neat pane-based playlist control.