Power standby effects on amp's aging and sound

Polk,
I lived in Tampa (USF) and NMiami years ago. I remember FPL which we called Florida Flicker and Flash. And yes, lightning is killer.

IF I lived there today, I'd have a whole-house surge protector installed. They are very good and fast and Not MOV based. So, they don't wear out.
Backing up such a device with a standard surge protector should be bulletproof. Than you've got cable and telephone to worry about. Another problem.

How much lightning do you get where you live? I live in the lightning capital of the nothern hemisphere (Florida) so I turn off and unplug my system quite often, and I've only gone thru one set of tubes in nearly 3 years. If you can leave your system in standby great, but I wouldn't leave it on unattended tube or ss. I wish I could leave my system on 24/7 best of luck.

Class D amps or Tripath usually stand-by at no more than 20W.

Capacitor life is function of ambient temperature. Each 10 deg C temp increase cuts life of capacitor by half. It is shown in many studies and published by pretty much all capacitor manufacturers. You can also find here: http://www.niccomp.com/help/presentations/AlumE-CapExtendedOperation0809-revA.pdf

on page 8 that this characteristic is same for different capacitor families. Assuming that good grade capacitor is designed to last about 50-60 years at room temperature it is most likely only 25-30 years since amps powered are often 10 degC warmer.

As for SS electronics being damaged from turning on and off - the only thing that gets damaged is power switch. Other than that semiconductors last pretty much forever - from SCRs doing millions of cycles in welding machines to Mosfet transistors switching 500,000 times a second under full load in output stage of my class D amplifier. Semiconductors have lifetime (everything has) but it is greater than your lifetime.

Other than power bill consideration you might find different claims on sound change. Many claim best sound after 24hours powered while others cannot hear any difference after 30 minutes. You have to decide for yourself. Take into consideration that you might need some time for your speakers to obtain full performance. Many tweeters, for instance, use ferrofluid that has some change of viscosity with temperature. My 6.5" midrange speakers use ferrofluid as suspension.

I keep my gear on all the time because of low power usage (class D amp) and very good overvoltage protection. It takes about 30 min for the speakers to warm up.

More damage is created by turning on and off than by just leaving the equipment on.
The downside as the op mentions is the cost of electricity.

The deciding factor to me is how often one is using the equipment.

I use my stuff every day, nearly all day. So i leave my stuff on 24/7/365 as the actual 'extra' electricity cost is under $10 a month (for my stuff in my situation)

If one only plays music maybe one night a week and on weekends.. Then turning it off during the weekdays makes sense.

As for stuff designed to be in standby.. I would leave well enough alone, unless you only listen very infrequently.

PS: some folks mention the idea that caps get dried out being left turned on. That has never been shown to be a real event. just a theory. (if you wish to counter this claim, please do provide a link to the scientific testing, not some audiophool website claiming it is so)
The fact that turn on and off is more damaging to electronic equipment than leaving on all the time IS a proven fact, easy to Google mean time to failure and read up on it.