This is only important if your salvation hinges on Mary’s sex life
That's no so, Rn, on two counts:
First, a thing can be important, even if it is not essential to one's salvation. For instance it is important to observe the Ten Commandments because they are part of God's word, even though flawless lifelong adherance to the commandments is not necessary for salvation.
Second, God Himself established the spiritual significance of childbearing. He placed a curse on the woman's reproductive capacities, making this a sign of the ongoing reign of sin. "To the woman he said, "I will make great your distress in childbearing; in pain will you bring forth children." (Gen 3:16)
It is a reasonable inference that if this reign of sin is ending, there will be signs of the lifting of this curse.
After the first sin, in Genesis, Adam is to bring forth bread by the sweat of his brow; the counter-sign of this is the wonderful multiplication of loaves by the Man born to the the Bread of Heaven.
Eve is to bring forth children by the pain and distress of her body; a counter-sign of this would be the Messiah's mother, the Kecharitomene, being free of bloody anguish in the wonderful conception and bringing forth of the Child who is Conqueror of sin and death.