Thanks everyone for various thoughts/suggestions... I think my biggest takeaway here is that it's not unreasonable to escalate this to the power company and see if they'll investigate it. Even if I waited 3 weeks to catch a problem myself, they'd still probably do their own monitoring first to confirm it.
Adam, is everything that failed powered from your distro or are they plugged into Edison outlets that are part of the venue service, or both?
Most was on my distro which is tied into a dedicated 100amp disconnect, attached to the building switchgear... if neutral/ground were reversed I almost think it would be irrelevant. (Not "correct" by any definition, but they're effectively bonded at the other end... Still, I feel like this comment might start a flame war.) Also the problems happened during times where overall load was trivial, so that probably eliminates insufficient neutral. I usually check the meters anytime we're hitting things pretty hard and never noticed voltage issues. We were just programming some LED lighting one evening and noticed two lights went out and the laptop wasn't charging anymore...
I'm not aware of issues elsewhere in the building but all network components are on surge/UPS... most devices including phones are POE, and the POS terminals are probably pretty rugged. We've had a LOT of trouble with light bulbs burning out in the event hall but they're fancy halogens and the prevailing theory is loud music vibration is killing them. I'm not sold.
The Ashly amp going out is the most troubling. It's one of a pair that share a standard dedicated outlet. One is fine and the other goes into over-current protection on all 8 channels even if nothing's connected; even channels that have NEVER had a load attached. Could just be a bad egg. The amp brags about multiple levels of protection, but specs say 120VAC +/- 10%, which isn't a ton of wiggle room. (Also troubling is I've left voice mails for Ashly on Saturday and Wednesday and haven't heard back... must be vacation week?)
So anyway, I'll talk to the owners about getting Xcel involved. Thanks!