I don't notice any difference in contrast without the light on, blacks aren't any blacker or whites whiter. The improvement was obvious between K2 and K3. I'm also not interested in the light and dislike touch screens, why should I smudge up the screen I'm reading from by touching it? Everything has to have a useless touch screen nowadays or the masses won't "touch" it.
So for me, the only advantage coming from K3 would be the higher resolution which I'm not sure is worth the price.