Mike - I really like what you came up with. Wish I had seen your 8x10 before I started building my new 8x11 (lost my basement space to my kids but gained bedroom....long story). Mine is similar, with an outer loop mainline and a connected inner loop. All interior space is yard and a city. I'm going lite on scenery. Because of already-expected boredom, I'm adding an elevated level, so at least I'll have the ability to run three trains.
Great job. Makes sense that you're a mechanical designer. Great use of space.