I have been a stickler about keeping power cables away from signal cables...on equipment ?

"I have actually rewired ( or had rewired by a tech ) a different path separating the power line to the audio line within the chassis, and hearing a cleaner background when listening to music through these products afterwards. "

Two comments:
1. Have you compared identical stock and rewired amps? If not, then you have no firm basis to demonstrate, at least informally, that there has in fact been a difference sonically. This is not so much a challenge to what you discuss in terms of hearing a difference, but an encouragement for you to test your own perceptions. Just as it is shocking to hear that there are no sonic differences between broken in and warmed up gear versus new and stone cold gear, so also you may be shocked to discover far less of a difference than you believe.

2. It sounds like this was not a truly apples to apples comparison, if the tech changed the amp in any physical way in regard to the power path. If there was any change to the power pathways, i.e. added wire, then it would not be demonstration of proximity, but of altering the power pathway. It would be interesting to learn whether the power layout was or was not altered. It depends, I think, on what you mean by "rewired a different path". :)

Finally, this could be a nice enhancement to amps, should it turn out to have efficacy when compared to a stock amp. Yet, the principle still would hold true that any given other amp of any particular design could outperform it. If you compared the rewired amp to, say, 6-10 others and found the rewired one consistently superior in a variety of systems, that would be impressive!  

I'd venture to say that it's all due to design, packaging and costs. Some makes will go so far as to put shielding, covers and walls inside an amp to segregate sections so they pollute each other. 

It's sad to think that someone will go to the trouble of designing something nice and then when they figure out how to package it, they just cram it all in without regard to placement and interaction.

Wasn't it normal for some vintage gear makes to have the inputs on the side of their integrateds and receivers? I wonder what the reasoning was behind that.

All the best,
Nonoise

DS....I hear differences of great magnitude after a substantial warm up of a piece of gear, as well as upgraded fuses. Based on your writings, we are quite different in our opinions. It is ok to challenge me on what I hear or what I think I hear, as I invite any and all comments to this thread. As far as connections on the sides of product, I believed it was for convenience for when they were placed in a cabinet or rack, but it does make sense in what I am talking about.