There is a reason real estate is almost always a top choice for investments: there is a finite number of land on this planet, and it shrinks. The more land you own, the more valuable it becomes as less land becomes available. Supply and demand. Economics lesson ends.
Hauntings are often tied to land. So if there is a finite amount of land, is there a finite number of hauntings? I don’t do math (as the joke goes, that’s why I went to law school) but we would need to factor in the fact that while new hauntings may occur (let’s just say due to violent death of some kind, like murder) we would also need to factor in mediums that help lost souls crossover. It would seem that if we have mediums crossing souls in greater amounts than we do have violent deaths it would seem that at some point, all the paranormal community could look to is residual haunts. We would hang out at Gettysburg waiting for the ghosts to recreate the war because that is all that is left. Or the paranormal community as a whole would become a bitter war zone any time there was a violent death that a person wanted investigated.
I am not a fatalist but I really hope this is not the paranormal world we have to look forward to.