Buddy pass riders in first isn't going to happen unless the plane is completely empty or its international. Everyone and their cousin can get a free or cheap upgrade now. Those empty first class seats will become empty coach seats by departure time.
Look at it as how many total empty seats there will be on the airplane, and that your buddy pass riders will get the worst ones. That empty first class seat is going to be an empty middle seat in the last row of coach next to a screaming baby by the time the gate agent gives you a boarding pass.