It seems intelligence and spirit have fundamentally the same meaning: one speaks without distinction of human intelligence and human spirit... intelligence signifying what proceeds from human intelligence, and spiritual what comes from the human spirit.
From this objective consideration, and as is often the case when there are two synonymous terms, other meanings have been superimposed. We say intellectual, for example, when we wish to say non-manual, or university professor, or abstract, or someone whose feet are not grounded in reality, or even “mind-aching” (prise de tĂȘte). The same diversity exists with the word spiritual, which sometimes means humorous, or religious (this last term is in my view a quite equivocal falsehood), or even divine (“Gods” spirit), to distinguish between divine intelligence and human intelligence, etc.
As far as the distinction made by editors in their “Spirituality” collection, we have here, I think, a mistranslation (which I pointed out) between spiritual and religious. Yet, fundamentally, there is synonymity. I see here on the one hand a type of marketing gimmick which seeks a label which does not ruffle anyones feathers; on the other hand, one must recognize that these collections include everything and its opposite: religious considerations, psychoanalysis, astrology, clairvoyance, and what have you... Therefore, they include what purports to be a rather speculative reflection, which happens to correspond to the first sense of “intellectual”.
I think the term intellectual is not used solely because the connotation is sometimes pejorative or mocking in nature; the same is true for the term “speculation”, which would turn away the clients who claim to be non-intellectual and pragmatic, concrete, with their feet solidly anchored in the ground! Hence “spiritual” is much more consensual, and in any case the term is gratifying. In short, “spiritual” signifies astute and clever, whereas “intellectual” can signify pretentious and pain-in-the-neck, which is evidently not the best pitch.
In brief, spiritual sounds “authentic” whereas intellectual has undertones of “concepts” or “ravings”. It is a bit foolish, but I think that is why it is so; a bit as why red and yellow are associated to biscuits, and why few of them are sold in a blue package. :-)