Good rambling, Russ. It's always nice to hear from someone with first-hand prototype knowledge and inspiration.
Jeff - if you don't have a copy yet, buy John Armstrong's 'Track Planning for Realistic Operation'. Even if you never get into 'realistic operation', the general skills and methods of track planning are an excellent resource. Just last night I was flipping through and it reminded me of a couple tricks I could use in my current planning project.
PLUS, Looking at your space...just made me think of the example plan he includes in the last chapter.
ALSO, in reference to loop plans like this, one thing that does look strange (and has been alluded to in another post already) is open top loads. Again this comes right out of the Armstrong book. With a loop layout like a 4x8, at least the loads are always traveling the same direction as are the empties the opposite direction (assuming you run 'em that way). With a dogbone, the loads go 'both' directions.
I second the suggestion about making it a single track main with reversing loops (staging?) at each end and perhaps a yard and definately passing tracks along the way in between. I'd love to have your space! Don't settle...keep planning.
Galen