Well, when I do a simple Save As, and save the project file in a new folder, the Save As Dialog Box has a check box to 'Copy All Audio With Project'.
I just tested this to make sure I was correct in my recollections, and sure enough, it only copies over the audio clips that are actually referenced in the project.
Prior to the Save As, the original audio folder had 7 audio clips in it. After the Save As, in the audio folder in the new project folder, there are only 4 audio clips.
Bob Bone