Not knowing the AB SOP I can't comment about the adjustment for tailwind on downwind. Much will depend on what you're trying to achieve. If the target is to roll out on finals on GP, rather than below it, then surely tailwind will affect ground speed and therefore distance flown in a time and would need correcting.
Regarding MDA +50': MDA = never go below altitude. I assume the MDA set for the approach is rounded up from the actual MDA e.g. 576'(chart) = 600' set. Therefore the a/c does not bust the MDA, so why add any extra?