Rod and main bolts-replace?

"The other, less-often heard school says if they look OK, they're already pre-stretched and have proven their integrity by not failing."

I would say this is misleading. A bolt that is over-stretched, or whose material is not adequate for the intended use is not visibly bad..yet both will fail if asked to perform beyond their design. A torque wrench used on a bolt that has been over stretched will still reach it's spec in many cases. But it does not have the ability to maintain clamping force.

" Most bolt failures occur in fresh engines with new (read; defective) bolts."
It is extremely rare to have a fastener from a reputable company be defective. It is MUCH more common to have the bolt nicked, or not installed properly, or get torqued improperly causing premature failure. I would venture to say it's usually assembler error that leads to failures attributed to bolts. Not the bolts themselves.

I am one of those who replaces all rod bolts during every rebuild. I also install main studs or ARP main bolts in every engine like Len does. All mine get line honed after too. A freshening is not a rebuild. I do reuse them when I know the history, and they come apart looking decent.