"...But it is only a single postulate that is required, rather than the long weave of complexity required by the biochemical postulate. "

ummmm...now there is where I suggest you are hiding true complexity by rhetorical means. ..... You freely grant that the biochemical thesis is complex, but try to present the spiritual/conciousness model as 'simple' because you phrased it in one sentence. What I assert is, that in order to make that claim, there are many assumptions embedded logically in the statement, whether listed individually or not. You must assume things about the nature of 'spirit', from WHETHER it exists to how causation works with it, how it CAN operate a body, why it 'exists' at all, how 'different' conciousnesses are defined (that is, how mine can be different from yours)[which is easy to do with physical frameworks]), ...etc...

   You see, positing a 'spirit' to 'operate' a body is really little different than positing a 'God' to operate everything, and a "Son of God" to relieve us of our sins...once you decide it exists, YOU are in control of the characteristics, and ambiguities and contradictions are just handled by linguistic altering of the explanations. You just state "that's how it works", and it is impossible to prove you wrong. (As in, 'you can't prove a negative')

It's a funny set of ideas....I can see why it is tempting as an explanation for experiences that are intense, but hard to explain...yet it's also the sort of explanation that has no real boundries or rules to know whether you are close to 'right'.

Occam's Razor has to be used carefully, or it will cut you in awkward patterns!