I am a believer in the ability of power cords to improve the sound over stock, from personal experience. However, like most "improvements" in sound, it is really incremental, not "that new power cord blows me away." Case in point: I switched out the stock cord for an Audience Power Chord on my Plinius SA100 Mk. III power amp. The change made a noticeable improvement in the tightness of the bass. I was very happy with the change in sound and the Audience PowerChord in particular. Did it sound like a new system? No. Was it an improvement? Definitely. Is a noticeable improvement -- let's call it 10% -- worth $1500? Doubtful. But $400 -- sure. So it ultimately comes down to just how much you want to spend to chase that improvement on the margin. Several times I have dreamed of getting some expensive preamp or power amp based on hype and reviews, only to put it in the system and find that while there appeared to be an improvement in the sound, it was not worth the huge outlay to get that incremental change.
I think that in general, fixing bad room acoustics will get you significantly more bang for your buck than expensive cables, followed by speaker placement, new speakers, new power amp and new preamp. Doing the cable dance is the incremental fine tuning of a system that you are already happy with. Luckily, since I will never, ever purchase a $20,000 cable of any type, nor do I know anyone nearby who would, I will be kept blissfully ignorant of whether such a cable will "blow me away." :)