That's a good idea, but I'd really like the explorer view to stay as it is.
Wouldn't a new branch be best suited for this anyways? Basically, a new entry between "Playlists" and "Computer", likely titled "Favorites". You could add (virtual) "folders" and "bookmarks" much like favorites in a web browser - except that bookmarks aren't, of course, just items but show all their files and (system) subfolders right there in the tree.