Well you keep thinking that there's a "genuine placebo effect at work at many circles whether old or modern" and i'll know otherwise, this may be true of almost all modern ones but i can assure you it's not true of the Ancient ones, if you really think this why have such a big interest in the subject? surely it's a love of the mystery and feeling of the places [you can feel at the places all the mysterious ritual that went on for sometimes 1000's of years, lots and lots of Ritual goes on in all Ancient cultures, and it's still the reason people say churches "feel" nice even in our times].