Should an audio system be left on at all times?

Actually, I asked about both longevity and performance. While some of us may be able to replace a system when it breaks down, I probably will not be able to replace my system with anything comparable for a long time to come.

Is the general consensus that I should keep everything except the tube preamp on at all times due to the high frequency of usage?

I'm hesitant to declare that we have a general consensus. But in terms of reliability I would say the diversity of opinion we have seen is consistent with the opinion I expressed that, considering your frequent but not extreme usage patterns, you won't be going too far wrong either way.

In terms of sound quality, optimal warmup time is going to be system dependent, and probably listener dependent as well, so if you choose to have your system off during the day see if you notice continued improvement in sound quality following whatever warmup period you choose to use initially.

Perhaps this is a bit of an anticlimactic conclusion in view of all that has been said, but I think that any conclusions beyond these simple ones are unprovable, are probably not universal, and in terms of longevity probably don't make a lot of difference anyway.

Regards,
-- Al

Complex systems fail more often then simple stuff....like hammers. Failures can be simple or complex. Also, complex systems are LESS fault tolerant than simple systems.
Complex, integrated circuits....Pentium is a fine example....
are subject to failures caused by heat and electromigration.
Electromigration is when a conductor 'crawls' under the influence of flowing current. Conductors ALWAYS fail at the point of thinnest metal, usually over a 'step'.

Also, complex systems are LESS fault tolerant than simple systems.

I'd add the words "everything else being equal" to that statement. The complex system might have redundancy and fault tolerance designed into it, while the simple system might not.

And I'm not certain that the statement is true even with that qualification. For instance, if anything in the signal path of a very simple amplifier goes, the system doesn't work.

Regards,
-- Al