Too many districts mean high costs because of the need to communicate between all the locations. Shipping parts from state to state is not cheap.
Now be careful not to go too far. I wand a few experts in the B1 scattered around the country - I don't want someone to be able to bomb one office/factory and we lose all ability to modify/build the B1. However there needs to be a balance.
Better would be if two districts produced B1 parts, and then a different produces tank, and then still another is doing ... That is every district should have something, but no one project is everywhere.