Well, studying cold reading is very useful to teach us about the brain/mental processes and to educate people.
"Poltergeists" need to be studied, as it is an observed phenomenon and scares many people whom it happens to. So far much of it has been explained in terms of known science, of course, so people can feel more at ease in their own homes. Some things, however, still elude complete explanation, so the research continues. The aim of such research is not to prove such phenomena are "woo" or to debunk them, it's simply to study the phenomenon and see what can be done with the data in scientific analysis.
It'd be completely false for anyone to suggest that we currently know everything about the world we live or our mental processes, so we keep studying, experimenting, questioning with the best scientific methods we have.