My immediate thought was to point you to the thread on aphantasia, but I see when I hunt it down that you already commented at the time that you didn't think it applied. Might be worth another look, though. And if you google, there's a ton of info out now that didn't exist at the time:
http://giftedissues.davidsongifted....9849/Re_Aphantasia_How_to_be_blind_.html

That thread was a revelation for me. I'd always thought my family were extreme off-the-charts visual spatial (and they are), but that I was just "normal" in comparison. That article started a conversation that made me realize I have no "mind's eye". At all. None whatsoever. It explains so. much.

"I didn't think you meant it literally!" Yup.

I do believe that the guy who wrote the original post cited above is dealing with a range of additional issues - IIRC correctly, he had problems with memory, sound and some other things which don't seem to be an inherent part of aphantasia. In my own case and most others, the term is usually used to describe just that missing mind's eye piece.

We never tried the Q-bitz version where you turn down the card; I imagine my results would be similar to yours. Playing with cards up with hyper VS-son, I found we had diametrically opposed approaches. I would look at the card, figure out the first cube needed, describe it in my head (e.g. "white triangle, apex in top right corner"), place cube, and then go back to the card to figure out the second cube, etc all the way through. No real sense of the overall design. DS would stare at the card, memorize the picture, the re-create it as a whole, usually without ever looking at the card again. I was actually often faster than him (he has slow processing and fine motor issues to boot) - but his approach could be scaled up to almost any level of complexity, mine could not.