One time, my dad was doing a deep clean of his house and very briefly set a PC monitor on his front porch. Someone hacked the VGA cable off of it, which was built in at the monitor-end. A good VGA cable has shielding and all that jazz, so it must be at least a little valuable...but on the other hand, I can't imagine someone investing the time to make something out of the cable as part of a business model.
With power cords, there is probably ten or twenty cents worth of copper in the lines.