Even a UPS is probably overkill. A Power Conditioner should be sufficient. https://en.wikipedia.org/wiki/Power_conditioner

Because some of these venues also run lighting rigs in the order of magnitude of 100KW and probably don't have the space/money/expertise to install a UPS with that power capacity.

Would lights need to be run on the UPS, or just the audio equipment?

A single loudspeaker in a line array can draw up to 24A at 240V [0]. Even a very small rig of 6 speakers would require over 30kw. A 50kw UPS [1] can be purchases for a very affordable $25,000 in 2016 [2]. When building a performance art venue in 1960 or today, a technical ground is a much more suitable option than a UPS.

[0]: http://www.meyersound.com/sites/default/files/leo-m_ds_a2.pd...

[1]: http://powerquality.eaton.com/Products-services/Backup-Power...

[2]: https://store.fgcupssystems.com/products/eaton-93pm-50kw-480...

Audiophile Mistake #1: Proposing a sensible solution to a problem which doesn't exist.

Like wooden vs. plastic volume knobs? :)

http://bobbyowsinski.blogspot.com/2012/05/485-volume-knob.ht...

It's not completely outlandish to imagine that noisy power could cause noise in the audio output of an amplifier.

I would hope that any good quality amp would filter the incoming power, though.

Yes, if it does, it's because of crappy (eg cheap) design. Any amplifier designer should assume that the mains power is very, very noisy.

I'm guessing that good quality amps for the install market are designed to be part of system where these concerns are taken into account.

My thought, exactly.

With a dual-conversion UPS, I don't believe that there'll be any noise from the power grid.