Hi Luke. Very interesting post. I will keep my comment brief because it's late here (Japan) and I need to go to sleep, but this is a subject that has always interested me. Sacred Geometry. On one hand, I have a feeling (I never asked them) that my Zen teachers would have said pish-posh, sacred geometry is trying to divide what is indivisible, describe what is indescribable, give name to what is nameless. And so on. Perhaps you can imagine. But that is Zen. In some ways, Zennies are the atheists of the Eastern world. Other schools of Buddhism here in Japan place some importance on symbols like mandalas, cultivating in Tibetan Buddhism which places tremendous importance on these symbols and patterns. Me, I don't know. I take a balanced approach and keep open to both ideas.
Hmm...it's an interesting topic to think about.
As to the Sri Yantra itself... I don't know. Like you wrote, it's impossible to say for sure. A lovely pattern though. There is something very attractive to these kind of patterns.
Anyway, sorry for the rambling thought. I will read the posts you linked when I wake up.