Lifespan of a quality solid state amplifier?

I am still (as a backup) using some 25+ year old SS amps and they still work fine other a higher noise floor due to aging caps in the pre/amp sections. While I don't think this is unusual, I would say the most amps of either SS/tube nature are pretty reliable. Other than tubes themselves, the main components that age are the capacitors. Strangely two factors can effect their longevity, one is heat-which would logically take a bigger toll in tube amps or class A biased higher power amps. The other killer is lack of use as the caps will dry out. Many people advocate using a Variac to bring power back to an amp that has been idle for an extended time to bring the caps back up to life slowly as a sudden rush of current could blow them. I've also noted that amps with several smaller output caps (as opposed to fewer but larger caps) are less susceptible to aging -don't know why...