Non-current limiting power conditioners

I could see spending $400-$500 on a nice used conditioner

This could get you a new APC H15 conditioner that is rated around 1.5 KVA and which as been tested to ensure it can deliver high current to power amps and UL rated to boot. Although this APC is an industrial pengineering company used by IBM/Sun/Oracle/Google and many others for data servers - this particular model has been deliberately designed for audio applications. Apparently they saw a market niche where profit margins are very high and all they had to do was reconfigure their design. Since they manufacture huge volumes of these power conditioning devices for industry I suspect you get amazing value that would not be possible if they just served teh audio market.

FWIW, Several of the suggestions do not regulate the output voltage from main
swings like the APC H15 does. This means if power sags during heavy loads or
when your AC comes on then these devices will not boost the voltage output to
compensate. Sagging voltages is one of the reasons that electrical equipment
can end up having a short life - in some cases it may even affect performance.
(The H15 is actually the basis for a Rotel conditioner RLC-1040.)

Why spend $500 just to get a glorified power bar with MOV's and filters when
you could buy something serious (even at this entry level price).