(See the best response by Ter13.)
How are some of you handling complicated (graphically) maps? What about saving and loading global map state?
Best response
I've seen the majority of the code behind the more complicated games on BYOND, and I can speak up about this. Generally speaking, map states aren't being preserved, so that answers your second question.

For your first question, largely speaking, graphically complicated maps are painted exactly the same way that small maps are handled, by defining each variation of turf and object in a file, compiling, then using the object tree as some sort of swatch index.

If you want some hints on a better way to manipulate the map editor, take a look over at this thread:
Thanks for the paint on map type tip there, I totally forgot about that.

As for the other issue, we should speak in private a bit more about my intentions as I am curious on how to efficiently save any non static changes to the world (not the entire map).
Take a look at the argument in this thread:

I detailed a saving and loading schema for maps that was pretty damn fast. It's a shame The Magic Man never saw eye to eye with me on my results, but my approach did in fact seem to trounce his quite soundly.

Of particular interest will be this post: forum/?post=1450705&page=2#comment8726752

Wherein I show off some test results of the particular saving methods that were in dispute.

You may recognize some of the techniques I detailed here, as they were influenced by some of your and my private experiments and their findings.