Are you running with or without mudguards. The spray and salt will go further without mudguards to contain it.
Those rotors may clean up using a dremel style tool with a wire brush on the end. But beware, it's a horrible attachment to use, bits of wire fly off the brush and get everywhere, including sticking in your clothes. Wear eye protection! If you don't have a dremel style tool then steel wool may work if you haven't left it too long (and the longer you leave it, the deeper and worse the pitting gets!)
As for gritting, I believe standard policy is to spread at 4C or below, so you'll often see salt all over the place when there is no frost.