no discs have nothing to do with the amount of brake dust generated, as far as i am aware anyway. the only factors to take into consideration are; brake caliper force i.e 2/4/6/8 pots, brake pad composite (fast road pads, normal) and how hard you are slamming on.
in answer to the brake area point, i suppose in theory you do lose a small amount of area but i suppose that this is balanced off against possible brake fade by the brake discs and calipers getting too hot?