For pure physical based mats I believe it is intended that the specular setting is not changed at all since in nature it is fairly constant. I assume its there to allow us to create interesting and unnatural mats. For me the spec settings caused the most confusion. In Reyes type render engines like Firefly spec is handled by highlight size, intensity and reflectivity, in PBR its handled by roughness and metal parameters which then calculates the highlight and reflectivity components itself. Because the PBR calculations take into account energy conservation (light out <= light in) it makes it much easier to make realistic looking mats.