Thanks very much for your responses, it helps to build a picture for how things work in the ATC world (I am more involved on the airport side).
Any comment on my second point regarding the hipothesis that it is impossible to achieve double the departure capacity of a single runway from a two parallel runway system (assuming the required runway separation for independent departures is in place), due to the reduced range of possible tracks? (Deps from one runway conflicting with deps from the other)?