Power cables are an interesting issue. I went ahead and changed out a few power cords on high current devices like my power amp. I also changed the one attached to my 50 Panny. I can't say I heard or saw any huge difference. Prior to this I had installed a dedicated 20 AMP line and use some fairly good voltage regulation.
I think that a power cord for the "last three feet" without other considerations may not be a best use of funds.