NB: My recent research into Astrology has lead me to place a great deal of importance on the so-called “Arabian Parts”: i.e. Part of Fortune, Part of Spirit, etc. It appears that the whilst the rest of the horoscope talks about generalities, the “Parts” supply details about specific subjects. In my personal experience, the Parts can be the deciding factor as to why two people who are born on the same day in the same hospital half an hour apart (= a difference of 7.5º in the Ascendant) can have completely different personalities.
My working hypothesis is that anyone who has a natural talent for the occult, will find that their “Part of Spirit” will form one or more major aspects in a significant area of their chart. The precise details thereof will indicate their own particular spiritual path.
Crowley
Crowley’s “Part of Spirit” was in his 6th House (Capricorn), and Square to both his Caput et Cauda Draconis. This would seem to imply that to him, expressing his spirituality was a routine matter for him; that it would be natural for him to see himself as a leader in this regard; but most importantly that he was driven by a compelling sense of both destiny and karma. His assumption of the role of Prophet of the New Aeon was his attempt to incorporate them into his spiritual life. Had he not done so, they would have been powerful forces for causing him trouble all his life.
He also had the Moon in his 9th House, which would imply he would naturally have a talent for astral projection or psychism generally.
Paul Foster Case
Case on the other hand has a far more subtle astrological chart. His “Part of Spirit” was in his 9th House (Scorpio), in conjunction with Mars in its own sign. Hence it would be natural for him to turn to psychism and mysticism. He would have had great drive to do so, although it is also likely that he went further in his spiritual quest than he ever publicly revealed, even to his confidantes. Yet despite this tendency towards secrecy, he still felt that he should be communicating his thoughts for a living: hence his founding of an occult correspondence school, which he felt would be a vehicle for achieving more ambitious things (“Part of Fortune” conjunct Mercury in his 6th House).
Sol Ascendans - The Website of Alex Sumner 
Very interesting article! My favorite text of Paul Foster Case (and Michael Whitty) is “A Dissertation Concerning the thirty two paths of wisdom”: http://www.hermetik-international.com/en/media-library/kabbalah/paul-foster-case-and-michael-whitty-a-dissertation-concerning-the-thirty-two-paths-of-wisdom/