In my experience, yes PC's do make a difference, but I have not yet reached the point of diminishing returns. I think it is a personal matter where you want to spend your $, and when you are finally satisfied to just listen to music. I have a fairly resolving system, although not up there with many of the folks on this forum. For me, the CVH cords were a significant upgrade and have performed sufficiently so that I have not yet been tempted to upgrade. However, I am currently auditioning speaker cables, which in my opinion make a much greater difference. I also upgraded to dedicated circuits (one for amps and one for digital) which also made a significant difference. I would rate the significance of system improvements as follows, although there must be symmetry with regards to the level of performance from each link in the chain:
speakers
components
ic's
speaker cable
power circuits
pc's
YMMV - Tim
speakers
components
ic's
speaker cable
power circuits
pc's
YMMV - Tim