Interesting points. The creative process, indeed, is different from one text to another.
In popular narratives it is diluted in the endless retelling (Hamsterbait, Satanus), and the individual work of any "author" becomes hardly perceptible.
And sure a number of agendas can be detected (Satanus, Gretchen, Tetra)... I found the way Tetra put it especially illuminating :
they also had political motives, but were most likely in total denial about it and in mentally discontinuous frameworks regarding it. they accepted the premise of jehovahs existence from childhood, and crafted all their stuff around it.
Almost everything in human speech and behaviour can be described as the interaction of desire and structure: the flow of desire running across/around the extant linguistic / cultural structure, being diverted by it and yet modifying it constantly like a stream its bed. Beliefs are a significant part of the structure.
Altered mental states (as jgnat and nilfun referred to, in a very different way), however induced, may be part of the tricks through which the desire succeeds in modifying the structure. Ezekiel would sound like a good candidate to me, and he is exceedingly creative. But there again, this applies only to a small portion of Bible texts -- most of which rather appear as the product of a very lucid, both pious and creative writing.
Test oracles (Tetra) are well attested in the ancient Israelite religion (ephod ritual, ordeal, Urim/Tummim) as a way to have God speak but they are not highly creative from a narrative standpoint, since all you get is a "yes" or "no" answer (which can help in a critical moment of the story but is not what the story itself is made of). I had never thought of Tetra's suggestion, i.e. using it to validate a text though... and I guess any good story (perhaps the major keyword being "entertaining," as Satanus put it) would somehow pass the test...
Whatever the strategies, it seems to me that the human mind always manages to believe in its own constructions, but never solidifies them to the point where they would actually become unchangeable. Creative faith appears to work between those limits, always finding its way between the obsessional efforts to "close the canon".
Am I wrong in expecting Ross here?