One other thing to consider with specular is that the more specular something is the less diffuse it is. So basically if x amount of light hits a surfaces then some is absorbed, some is reflected as the diffuse component and some is reflected as the specular component. You never get a surface with 100% diffuse and 100%…
Another thing to consider when perusing a particular look is that specular can also be judges or quantified by how much contrast there is between the local color (diffuse) of your object and the highlight itself. So if you have a lighter object a brighter spec might be more desirable, and if you have a dark object a duller…