The fine steel wool definitely will liven up a dull finish. I've used it on my red performer and on a couple of standard black grills as well as my WSM. The dulling seems to be mostly just dirt and grime, although I know that the finish on some of the Weber grills oxidize over time - hence the 30 year old kettle that now looks gray.
As far as the scratches, like George, I doubt the steel will will knock them out, but it could lessen the noticeability of the scratches. If they really bother you, use some plastic garbage bags or news paper to mask out the non-affected areas and then hit the scratches with a few coats of grill and stove paint.
Pat