Yes! Good Mains Cables DO make a difference!!
Possibly THE most cost effective upgrade for any truly great hifi system, Naim Audio's Powerline can (in compatible systems) offer a bigger improvement than even the great Flatcap XS power supply!
Whether you run it into your component direct, or feeding a high quality star earthed mains block (no filters or surge protectors please!!) and your system will gain an extra layer of focus and improved dynamics.
Check out the Powerline here!