Interesting, inrush current having an affect on cap life. That is also not any kind of spec on caps. What is a spec is time, temp and voltage.
On tubes, they also do not like heat, or voltage spike/changes. There are devices that stop inrush current on tubes, power them up slowly.
On switches a lot of new stuff doesn't have one. If it does have a power switch, it's not really a power switch, but a button that puts the unit in stand-by.
My system is all plugged into a Furman, I just flick the mag breaker off when not in use. Don't use any of the switches on my gear. However, my HT system has power all the time.
Sound wise, yes, leaving it on is best. Not sure it's best for longevity. Also think what Paul is saying when using perfect power with a regen unit, there may be less of a need to power down.