I agree that a streamlined way to export video clips to Lightroom and import them back to Premiere Pro is very much needed. Lightroom is very powerful for color and density work and at least ten times easier to use than SpeedGrade. The conceptual vocabulary for editing color and density in still photography is much more logical than its counterpart in the video/film world. Curves, shadows, highlights, the white balance eyedropper, and tint sliders make way more sense than the "crushed blacks" lexicon of the video world or the "three-light timing" lingo of motion picture labs.
It shouldn't be that difficult to add video import/export to Lightroom.