So some things I thought were interesting from the Ebay stats
1 - the top 8 models making up ~50% of sales there was a 70:30 split between ones with some automation, such as Aperture Priority, and full manual.
2 - The release dates of the top 8 were between 1971 and 1981, with 6 of the 8 being between 1976 and 1981
3 - Manual Focus models way outsell AF ones
From this it seems a new SLR should probably be a manual focus fully manual operation, with an aperture priority 'sister' to go with it,
I think the lack of sales for AF makes sense, older cameras are/were valued for construction, durability, craftsmanship, etc. Late 70s-early 80s retained some of those classic natures with some tech inside. AF ones were valued primarily for technology. Fine construction, durability, and craftsmanship does not necessarily change over time, but tech is always valued in comparison to the latest and greatest so it would make sense that once cameras went plastic, tech became the primary metric.