One thing I found very valuable in The Structure of Scientific Revolutions was a quick shortcut to telling if a field is doing "normal science" or not. If students are taught with textbooks distilling the field's important insights in a readable form then it probably is. The originator of an important idea is rarely the most skilled at expressing it to newcomers, but if your field can't tell if a rephrasing of an idea is still true or if it is more concerned with the prestige of the founders than the amassing of truth then it will tend to use original texts.