Many (but not necessarily all) people who sell this type of paraphernalia or services are con artists looking to make a buck off of desperate people who are looking to make sense of their lives in places where they won't.
Tarot cards / systems of interpreting them are a good window into how human minds work, and insofar as that's relevant may indeed be useful. Many of them are also pretty.
The tools of rationality, collection of evidence and the scientific method are the best ways we have yet developed to further our understanding of the world. They are not (nor ever will be) complete.
Blanket dismissals of the metaphysical are as baseless, and no more worthy of consideration than, the simplistic assertions like "the sun revolves around the earth... because we say so".
There might be some things we don't understand, like the 21 ounces or whatever that one loses after death. Very interesting, so far unexplained, yet documented phenomenon. Similar things can be said about certain reincarnation and near death experiences - how could they know some of the stuff they do? Maybe there are yet unidentified physical explaination, maybe something else. I am looking forward to answers either way.
For stuff like tarot, there are probably some interesting body language or physiological things that are behind it. I have a hard time believing most stuff like this and mediums. However, that could be that there are a large number hacks obscuring an extremely small number of people with actual talents. I'm also looking forward to any research finding on these topics.