Actually I don't know that this is the problem, I finally modified my Nomad with the new LCD mod and it uses composite out yet the picture is much clearer than the picture on the Supaboy. Would RGB really make a difference? I find the picture on the Supaboy to be terrible, it looks more like the picture I used to get from RF cables in the early 90's, flickery, blurry texts and poor detail.
EDIT: That indepth reply was a great read by the way.