Its starting to look quite a lot better.

I usually use at least 20% antialiasing, preferably 33% and sometimes higher.

Each of those bands is a pass made by the rendering engine.

You can use wider passes by typing the command EXPORTSETMPPP and hitting return. The command line will tell you the current Maximum Pixels Per Pass, which at default setting is 4000000 (4 million without commas).

Try typing 40000000 (40 million), hitting return, and trying your export again.

Try hiding the STRUCTURES(COLORS) layer.

That sounds like a really complicated operation.

What about consolidating all those tiny bits and pieces into larger png images in GIMP or some other bitmap app, and then importing the fully formed symbols as single entities?

Anyway...

If you want just one image to have a different origin import them all with the origin that is right for the majority, and then edit the one that needs a different origin from the Symbol Manager. Use View->Move origin to pick the new origin position while you are editing the symbol in the edit window.

Alternatively, you could just move that one symbol into a subfolder within the main one and import it on it's own with a different import origin.

Well, there are actually several ways of getting the shadows to behave themselves properly. That was only one idea, which may or may not work for you. The other way is to create a new sheet called something like CLIFF TOPPING and use it to draw a shadow-casting plateau that covers the entire area of the higher ground a bit like this.

Here is the FCW for you so you can show and hide sheets and see what I did. It might be harder or easier to do it like this. I don't know. Only you can tell what issues might arise, as the creator of the map.

And here is the alternative I described before.

I haven't even tried to imitate those beautiful colours you created, but these are just 'how to' examples ;)