High end AC plugs/receptacles...

ABSOLUTLY!

Yes, Oyaide and Furutech are worth every penny.

I have Oyaide R-1's and the WPC-Z cover. I think the cover is as or more important than the outlet. Never did I hear more difference than putting in the wall outlet and cover. When I added more R-1's downstream even w/ Oyaides outlet strip MT_UB
the change was nowhere near as audible and dramatic.

ET

if you can hear the difference, it is worth the price. i suggest having two power cords configured with two different plugs and iecs. you will then be able to answer the question for yourself what differences are or are not audible, with respect to connectors.

do not elicit opinions. do your own research.