are brake dust shields necessary

The other reason you want to avoid water splashing directly on the rotor is that if the brakes are really hot and get a good splash of cold water, it can warp the rotor. More of a problem with economy cars and their undersized rotors, but the K-H rotors are none too thick, either.

I've seen that cooling duct trick, I think on the Team Starfish Barracuda. You wouldn't want just a scoop without the duct -- it would just funnel all the crap directly onto the rotor. But routing the duct so it doesn't foul the steering or restrict the suspension travel looked pretty tight. I was just pondering louvers that face backward, to let the hot air escape...