Why does specularity and dual lightmaps only work with Parallax Mapping / Rim Lighting?

I tried working lightmaps and specularity into my Unity 3.5.6f4 project with Forward Rendering and Dual Lightmaps are right now the best solution (Directional Lightmaps and Unity 4.0 are problematic).

However, i can only bring nice specularity to Dual Lightmaps when the shader executes Parallax Offset or Rim Lighting. I guess these are a rather expensive commands, so i`m asking:

Is there any cheaper way to bring specularity to simpler shaders while employing dual lightmaps?

Is there anything else to adapting shaders except adding the dualforward parameter?

example screenshots:

standard Parallax/Bump/Specular (left), standard Bump/Specular (right) shaders with dualforward parameter added, dual lightmaps employed and desired specularity.

standard Parallax/Bump/Specular (left), standard Bump/Specular (right) shaders with dualforward parameter added, dual lightmaps employed and wide angle specularity.