Sethren, increase the scattering anisotrophy parameter to get harder edges & highlights near the sun.
If you want finer details in the volumetric layer, size down the details scaling parameter in the advanced material editor of the cloud layer. You can do the same for metaclouds. For metaclouds, you can adjust the "cover " parameter to get thicker clouds. Don,'t over do it, though, or the original sphere object will show.