Now that you mention it, I think I do recall that being mentioned years back in an article, but at the time I didn't pay much attention. When I was still working, career technician, we used to have sheets of the stuff that IC's, etc. came in on....Retired now or I'd snatch some up, probably be able to find it easily enough on line............Also, I recall the 400Hz thing........Don't see myself buying a regenerator any time soon though, unless I found one used on ebay :)
As for leaving gear on, as long as it is able to "breath" with good ventilation, and doesn't get more than warm, should be fine. Excess heat kills electronics. We never tested anything unless it had been on a minimum of 30 minutes, preferably longer, to stabilize. Test equipment was never turned off, except over long holidays.
My larger power amp tends to run hot , but only when I'm listening to music, so I picked up a low noise, 18db, 120mm PC cooling fan, built a simple frame for it and set it on top of the amp. Looks fine and keeps the amp cool no matter how hard I push it..........If anybody is interested, the fan is a Noctua......Austrian made, NF-S12A.......less than $20. Very quiet, barely hear it even in a quiet room. That with a 12 volt wall wart and heat problem is gone.
I don't know what your system is, but leaving it on, at idle, isn't going to add more than a couple bucks a month to your bill. I doubt that you'd even notice the difference month to month, gear off or gear on.