"Another of my metrics on the quality of an engine is Ebay price for a used one. The cheaper they are, the less they are in demand... "
Yes, agreed, and it's only part of the story. There can also be big demand because of the hi-po folks or other factors. The Dodge 6.4 Hemi is reallyu expensive used. I got more $ for a no-good 6.4 Hemi than I paid for the whole truck. Guy wanted to build a race motor and didn't care about the knock.
The 6.4 Hemi is an interesting example, when I rebuilt one I was very impressed with much of the design work. A thoroughly modern design in spite of being a pushrod V8. Lots of really good stuff that would have been racing exotica a few years ago. And a few specific quality issues and a need for special oil, that ruined its reputation.