Yes. Much like the concept of black holes, pulsars, string theory, etc. There's a lot of things in the world that have not been directly observed but assumed, proved by mathematics, etc.
I'm not here saying that there definitively are ghosts in the world. What I am saying is that culturally there's enough evidence to not discount it, and that there are theories (again, theories, not proofs) regarding the methods of measuring paranormal activities.
I can certainly relate to your romanticism on this one. An open mind is a good thing.
Now, we're getting out of my league with string theory and black holes, but I understand that there is, as you yourself said, much evidence in support of these ideas. But what evidence is there to suggest that EMF waves or temperature differentials indicate "spirits"?
To be honest with you, I can't point you at any subject matter that I know of that says "a high EMF reading means that there's a ghost here." I'm just not that up on it. I know what I've learned from watching Ghost Hunters on Sci Fi and reading a few books.