Vertical pan stabilize

I have some hand-held footage that pans vertically. The left and right sides of the footage change often so there isn’t much of a vertical plane to lock onto. Should I create spline key-frames for information close to the center of the footage as it moves up?

You can do this a couple of ways. You can either animate the shape before you track to hold onto key areas, or track and adjust as you go, OR you can draw a large shape and unlink the shape from the track and track everything that moves beneath your shape. It will all depend on what your end goal is as to which is best for you.