What is it about a church and listening to a pastor that makes it more sacred or holy?
No one made such a claim, so I'm not sure why you're asking.
Do you really need a third party to find your connection to God?
No, but our pastors are there to teach us and help us better understand Scripture.
Is praying at home and being a good Christian without the church somehow less legitimate?
Not sure how you define "being a good Christian," so it's hard to respond to that question. Simply praying at home doesn't make one a Christian. At the same time, as the late Keith Green used to say, going to church doesn't make you a Christian any more than going to McDonald's makes you a hamburger. It depends on your relationship with God.
It doesn't make sense to me that a building constructed by humans somehow amplifies your attunement to God.
Again, no one has made that claim. We go to church for fellowship with our fellow believers, for communal worship of our God and to learn from His holy word. In my church, we use the building to host monthly free community dinners, concerts and the like - things that require a building of some sort. The building is not the church, it is just a tool used by church to do the work of God.