UPDATED: Merge-Delete Playlists v3.3
Merge-Delete Playlists will allow you to merge the track contents of two or more playlists or delete any number of playlists at once, including Smart, Genius, and Playlist Folder playlists. The merge feature will prevent the same tracks that may appear in different source playlists from being duplicated and has an option to delete original playlists. The delete feature only deletes the playlist; tracks, of course, remain in the library.
This latest version fixes issues running under Mavericks and fixes a problem re-enabling after a delete operation.
More information and download is here.