[quote=@Ashgan]
That said, Spirit probably branches out into a region of its own when the occult dial gets turned up, and at that point I expect things will be clearer.[/quote]

Exactly this. At these 'low levels', they overlap quite a bit. So, your concerns are completely valid. But when things move along and the occult encounters and matters become more complex, the difference between 'soul' and 'willpower' will be greater. Willpower is also for normal threats and conflicts that are not of occult nature, so there is another difference.