Powercords seem to generate the largest conflict. I used to not believe they could have a hearable difference.
I played around with realitively cheap powerline conditioners for about two years, and found they had an effect. Then i made some Pcs from good wire and ends. This December (2009) I tried a Pangea and the 9 gauge Pangea on the amp had a clear and immediate improvement in the bass. I was hooked.
I would not buy expensive powercords, but the Pangea at $40 up to about $120 for a four meter long one are about the same price as buying Belden wire and cheap audiophile plugs.
I have gone way upscale on Power conditioners, with a Furman REF 20i (used only $1,400. instead of $3,500.) but I doubt I would spend a lot on individual cables.
I am a 'believer' but not a fool!!! so the megabuck cables are never gonna be in my system. I have said, if one is going to spend thousands on a cable, better to put the money in the basic electronics first, and buy a 'cheap $100 to $300 cable..
Emperical evidence from a LOT of users says that cables can make a diference. A few folks who have tried say no, the do not. And a LOT of naysayers do so based on theory only.
The trouble is some folks have said (and bought) $600. Tice clocks that just need to be in the same room.. and claim differences.. so the basic premise of imperical testing seems to not quite be theere for all testers... LOL!
Tice is gone, but new flimflam stuff pops up all the time. Who knows what is real?
So, from one who has tried powercords and found a low, worthwhile price for the value of the improvement: buyer be wary!
A little is good. More can be good or foolish, depends.
I blew a few thousand on cables.. for the whole system.
A thousand for one? no way.. never.. I am too cheap!