I have seen certain hair such as by AprilYSH and Neftis that have a characteristic "translucence" to them. The geometry is ghosted and the strands very parallel. Is this what the first post might be in part about?

I have notice a difference between painted hair strands in a texture and sampled ones. The painted ones seem very uniform in width and distribution with each strand running from end to end on the geometry piece while the samples tend to show strands of finer less regular width strands that begin and end along the geometry piece and criss-cross each other to give an illusion of layering and depth. The painted hair also seems to often suffer from a low contrast tonality while the sample seem much more contrasty and to me more realistic.

If one is against baked highlights would one not need a bump or displacement map for the rendered highlights to look good?

Having started with Koz hair I have been sorely disappointed with most commercial hair I have bought. Strange translucence, obvious geometry (tubes etc.), overly regular strands, but most of all a horrid mat quality where blond is ocher etc. It is amazing how often I must purchase a 3Dream texture for a DAZ or other hair! Then of course is the issue of realistic styles as opposed to fantasy... there must be a market for ordinary hair styles? I see only a few such as ernyoka1's Comb Over.

My own aborted attempts at hair were done entirely in Poser. I took sections of ball prop and morphed them into shape and assembled them according to Geep's prop building tutorials. Then I used UV mapper to create a template and painted the textures using the methods shown in the pure post-work hair painting tutorials; lots of fine over painting for layering depth illusion and dodge and burn for baked highlights. The results were so-so so-so but it was a learning experience..