I think that as much as possible, links to the "upgraded versions" should include links to the original (the originals are public domain now in almost every cas

I think that as much as possible, links to the "upgraded versions" should include links to the original (the originals are public domain now in almost every case so this shouldn't be a problem). The only danger is if people don't have the originals for reference and think that details in the "enhanced" versions (that might be completely artificial) have more reality than they do; I don't think the historians have a gripe if promoting these colorized, upsampled versions is done in a way that also promotes the originals.