I'm also believer, but would not spend for aftermarket power cord. For me the magnitude of improvement isn't enough justified for money spent. $0 stock power cord will still have much better ROI.
Update power cord
I have a Rotel RB 991 power amp driving a pair of Vandersteen 2 ce speakers. t has a captured power cord now would spending a few bucks to have an IEC power outlet installed and upgrading to a reasonable cost power cord make a difference. I would like to smooth out the top end a bit.