Thank you very much, Mealea. It is true I'm a glutton for punishment.
This render is as good as it's going to get for this particular piece of the puzzel. It took many hours to get it, and it failed halfway through, 3 out of 4 times I tried. I am seriously well over 200 million polys in this one ZTool alone (and every piece of it is decimated as far as it can possibly go). I can't do Spix above 3, so I get aliasing around the edges, and I can't really say overall that this is how I see the whole thing in my head. Very frustrating. The models are good I think, but the file size has gotten so unbelievably huge and unwieldy that it's really become problematic to do anything more with it - so that's that.
Now, my challenge is to put the other pieces on top (in several separate renders) and make it all look organic. My fear is that when it all comes together, it's going to look like a badly assembled pastiche (rather than a dynamic scene that appears to have been rendered in one pass) - but I guess I'll find out soon enough.
If it works out, I think I'd like to print it full size. It's not going to read very well any smaller.