If I'm understanding you correctly (I necessarily had to read this at a rapid pace, I have about five minutes to read and answer), you are working on a specific issue - perhaps authenticity of the experience, trying to escape bullshit and get outside your own preconceptions. (If I worded that incorrectly, please forgive; as mentioned, I'm writing this quickly).
I that case, my advice would be, sure, use the tool as you see fit for your personal, individual, immediate goal - just don't confuse it with the training specific to the A.'.A.'. system, which has quite other goals.
There's a bit of psychological projection going on here: You distrust yourself and want to prove-up yourself, so you express this by distrusting the technique and turning a training exercise into a requirement that the technique prove itself to you. If your goal were, as you state, to enter into a more productive relationship with subconsciousness, then the most direct path is, in fact, to train your rational, verbal mind in the same language subconsciousness speaks, so that you will understand it when it speaks. Memorizing the lists increases your vocabulary of the language of subconsciousness.
@sinistralkool said
"...another part of my mind resists the former viciously, resisting any such attempts to 'impose' a system, and is especially hostile to the idea of adopting any set of symbols that have not arisen spontaneously."
That half of you is winning. Since you asked my opinion, I will give it: Why should this arise spontaneously? Where'd that crazy idea come from? Since when is communication from a suppressed, brutalized, maligned, neglected mind expected to be spontaneous and clear?
"But if the correspondences are natural or universal, why is it required to saturate the mind in those symbols prior to invoking the vision first?"
Natural yes; but not normal. We are distorted. Most of us are twisted messes on such things. We have (for example) habits of thought that are entirely normal to us, but not at all natural. That's kind of the whole point: The species as a whole has mostly suppressed nature, and the normal reflex of most people's intellect is to set us up to keep it that way. Ego wants to be king, and not have a competitor!
"Let's say Mars is invoked in the body of light, one sees a landscape that is of the correct colours, mythical creatures, smells, materials associated with Gevurah etc. Is the value in the exercise in being able to tune the mind to a natural reality or to be able to recreate an adopted convention faithfully, and ultimately, how could you tell the difference? Is it perception or recreation? "
Your question presumes that these attributes are incorrect. An "adopted convention" that is artificial - just somebody's arbitrary ego assertions - would be crap. That's not how these were obtained. - But I can't I imbue you with trust, where you plainly distrust. (PS - How you tell the difference is that, as you progress in initiation, you develop a deeper instinct or truth sense for such things, as you undergo changes yourself.)
You are so obsessed with the testing aspect. That comes later. Your obsession with it is still your intellect trying to stay in control. It's ego winning out and continuing to lord it over subconsciousness. Screw testing until later.
"My sense is that there's an intuitive knack that develops after a while of practice, but if that knack can't be systematised, where is the value in the common methods of testing visions qabalistically? "
If I had another half hour, I'd break down the illogic in this sentence. You actually changed topics mid-sentence, and then leapt to conclusions based on facts not in evidence. I advise struggling with this sentence a bit.
"It makes sense to want to be able to invoke pure forms of force, elemental or astrological, but I'm not sure why the test of the successful invocation of that force shouldn't be more peculiar to the individual. "
Again: BECAUSE IT'S NOT ABOUT AN INDIVIDUAL. IT'S NOT INDIVIDUAL. IT'S PREMATURE TO TEST UNTIL YOU'RE PAST THE PLACE OF IT BEING YOUR INDIVIDUAL CONTENT. YOUR EGO CENTER IS IRRELEVANT TO THIS. THAT'S ALMOST THE WHOLE POINT.
"I am particularly interested in the Sleep of Siloam, in contrast to the lunar sleep"
That's a 6=5 practice. You are still working on getting a starter skill on 1=10 practices. Nothing to stop yu from attempting, of course, and getting what success you may.