>NAS' routinely run just fine without it.

How do you verify your data to confirm that?

ZFS helps, and many people are okay with the risk of a cosmic ray causing a bit flip while data is in flight once in a blue moon.

I currently manage four NASes (two primary, two backup replicas). Only one has ECC RAM. And I'm okay with my setup.

ECC is great to have, but it is oversold by some as being absolutely required for all storage devices, IMO.

For truly important files (photos), I’ll take the slight added expense of ECC for a little more peace of mind that old photos aren’t being gradually degraded with every resilver or scrub.

Good point about ZFS. Having more than one copy helps too. ECC is great when possible.

Multiple backups.

How many files have you personally seen gone corrupt on non-ecc?

ECC originated first out of server grade servers. Self-hosting rarely hits that level of demand.

My first thought is the same way everyone's laptops and desktops and cellphones without ECC data do?

I'll share any more that come to mind.

Use a RAID5 and hope the write hole doesn't eat it all =(