When I first heard the analogy of the priesthood being like an umbrella, where the man holds the umbrella, but its blessings cover both men and women, I liked it, but I think this car analogy may work even better.
Which part of the car is most important? The engine, the brakes, the steering, the separate and little and oh so losable key? Can we even say? I don't think we can say which part is most important. Each part serves its function, and none can properly function without other connected parts. It is the key, however, that activates the car; it is not most important at it serves as part of a whole system, but it is absolutely necessary.
I think you can extend the analogy to making women the key in the roles they play, particularly regarding growing babies.