Please convince me if I really need to run a 5m power copper line segment next to one of the strips for the one area I can't really get a dedicated power supply to after reading this plan.)
You have several options apart from this one. You could site the power supply at the far end, or you could try large capacitor at the far end as well as the near end. But at the end of the day you have to see what works for you. Personally I would split the power supplies up to 20A a piece but I have no very strong conviction about this. Playing with large currents is more electrical engineering that electronic engineering.