I have the 50 1.4 D and really like it. Some of the cow pictures in my albums in the below link were done with this lens. If I had a a 1.8D I'm not sure I would upgrade. The 2/3 of a stop is less important now that the iso performance is so good.
I recently bought an 85 1.8 D and find the narrow DOF is quite adequate for my needs.
The new AFS version of the 50 may be a little less prone to flare, but I have not had significant problems.
"Cameras and lenses are simply tools to place our unique vision on film. Concentrate on equipment and you'll take technically good photographs. Concentrate on seeing the light's magic colors and your images will stir the soul." Jack Dykinga