Love your stuff. As a pastor, I would agree with your observations about prayer. I think that God is not a politician, and that numbers per se, do not impress Him. However, I do think that when large numbers of people turn to God, he is gracious to respond to them in some way.
As stated in II Chronicles 7:14-15 “When I shut up the heavens so that there is no rain, or command the locust to devour the land, or send pestilence among my people, if my people who are called by my name humble themselves, pray, seek my face, and turn from their wicked ways, then I will hear from heaven, and will forgive their sin and heal their land. Now my eyes will be open and my ears attentive to the prayer that is made in this place.”
There is a dynamic relationship between God and individuals and groups who pray to God. He is NOT of course a divine vending machine, but a Personal God who decrees his will and listens to us in the mix as well.
I do think that there might be some superstition to the numbers thing. Or just enculturation of American values (More is better!) when it comes to prayer. I also know that when a meeting or prayer event has a SMALL turnout, we are quick to quote “where ever 2 or 3 are gathered in my name, there I will be in the midst of you” Kind of a theological safety net for those who gather to pray in small numbers.
p.s. I do believe in the power of prayer- to change circumstances or to change me in the midst of them.