That's why I use my checking and unchecking method. It works great. I can start a smart playlist and while it's playing, I can search for other items to add to the list, simply by checking them. I can either have them repeat all songs, or only play each song once. It works well for me... YMMV.Ah yeah, that is another pet peeve! That would pretty good if play wasn't interrupted.
The iTunes music library search bar has always been pretty poor. You can't put in parameters to prevent stuff, or only search only artists etc.