Quote - Am I right in thinking that the ideal texture should be hand painted, from such a reference, rather than just photo-processed?

Pretty much and also note that just as important are nice, high quality bump/displacement maps. eg if you look at the above examples by BH, note that color detail, even in the unprocessed images, is very subtle whereas bump detail is very very prominent. Unfortunately most poser content makers go the opposite route and focus mainly on color textures while bumps are whatever they can quickly derive from a photoshop filter or two. This is why even the best poser artists, using the best poser textures and the best shaders still produce doll like results. See the difference: Without bump:

With bump: