In my opinion, for spiritualism to be documented effectively, a very abstract component must be lured out of one’s viewer–faith. A viewer doesn’t have to share the photographer’s religious denomination to appreciate the work; a viewer only has to have a smidgen of understanding, that openness of the mind. Without it, the viewer would not ‘see’ anything at all, no matter how skillful the photographer is or how convincing the image turned out to be.
For me, personally, I believe that spiritual documentation is possible. Although not a very religious person myself, I simply think that anything is possible in this world. In this case, however, a photographer must be fully immersed into the subject: He or she has to believe it. For it being valuable, sure, for any type of evidence towards its accreditation (or otherwise) must be kept and accounted for. It’s like graffiti, once rejected for its impetuous and rebellious nature, but is now considered an art form; spiritual documentation can be the same: it might not receive a great deal of following right now, but people would eventually see how its uniqueness can be translated to creativeness. And then, again, one doesn’t have to believe in its validity for it to be considered beautiful.
Intrusive? Yes, for the camera being present is like a perpetual intruder. I feel that it undermines the sanctity of the supernatural, and with popularity of image editors out there, a non-believer could easily discredit a photograph by referring to these software. Ultimately, manifestations must be experienced to be called true. A photograph is merely a medium to speak of its existence, and it is only up to the viewer to believe it or not.