I'm going to preface my post by saying I am not well read on psychology or NLP ideas and won't be commenting much on the subject.
When I'm saying Mentlism as mentalism I mean it in the way of Kreskin, Annemann, Osterlind, and to an extreme Uri Geller. I'm not saying mentalism should be used to scam people but as entertainer and performers of mentalism this should be the goal in my opinion. But as performers playing the part of a foreseer or telekinetic super dude, I feel instead of explaining away how things are being accomplished is a disservice. The performer isn't a mentalist at this point, they are more of a professor showing off their latest findings and curiosity. Which is fine! But I wouldn't label myself as a mental performer if this is the persona I've adopted.
I've kind of hinted at an answer toward the second question however just to expand a bit, the audience should believe that there is the possibility that someone was born with a gift. Why they are performing instead of using their powers for riches could be explained that it doesn't always work. This I would assume can help the audience relate more to the performer and remind them that they really aren't all knowing all the time. Everyone has made mistakes, everyone has had a failure in their life, and when someone who has extreme powers shows vulnerability they become more human.
In regards to psychology, etc. I'm certain the course is rigorous but as applied to magic its negligible. Psychology as a science I think is, how do I phrase this? I think psychology and its cousin sociology are great supplemental courses in fields like neuroscience, I'm sure people who actually take the course consider it equal to other sciences. But I can't help but compare psychology to a D-lite effect performed by a magician and calls himself an artist.
Hope that helped TeeDee,