I agree and said before, a rattle can is the way to go with the spatter effect, a toothbrush wont get the effect your after Rob!
I used a rattle can on the Y wing and X wings builds, and it really does work well, i played with distances of 12" to 24" roughly, and the gradient change was superb, the speckles just fall on the model pretty much dry, leaving the finest grain feel, which IMO, is the way it should look, a toothbrush, would be very rough id say!
Youll have to stand on a chair to drop it on the upper dome i guess, so mind those health and safety laws :lol
lee