EC, I echo those who recommend aerobatics, tailwheel or float flying. Those will be the very best to help you improve hands and feet skills. A CPL course will just do the PPL skills to a higher standard, which may not be what you're looking for.
I suggest away from an "advanced PPL" course, unless you know it contains exactly the training that you know you would like to have. Even taking an hour a month of good aerobatic instruction, while you continue regular PPL flying, will make yo a better pilot.
Pick a skill, and develop it, then go one to the next. Though you won't be flying aeros in the weekly rental Cessna or Piper, the skills of precise flying within the "normal" realm, can be practiced when you fly general maneuvering.