Yah, for me it's an open question whether I would run shod on trails that were too gnarly for bare feet. So far my only compromise has been with temps, and even there I've been willing to push the limits of comfort a bit in order to stay bare. Only time will tell, but it seems to me that if a trail is too tough for bare feet, then it can't be much fun to run over shod either. I ran over pure gravel last summer, and it was tough going, but doable, and I assume if I did it enough I would adapt. As long as you can mix it up with smoother surfaces where you can get the need for (relative) speed taken care of, I think I could deal with the slower paces that tough surfaces require. I'm not really a performance guy, more of a purist I guess. But theory often changes in practice. So far my trail practice has been limited, like yours, to the tame terrain of the Upper Midwest.
BTW, Sid et al., picked up these items on sale today. The tech whoredom continues unabated, but I think this will do it for now:
http://www.rei.com/product/835243/rei-winterflyte-pants-mens
What could be better than saving half off? Saving 51% is what!
http://www.rei.com/product/779938/mountain-hardwear-wicked-lite-double-t-shirt-mens
I got two of the t-shirts, one blue, one yellow, one large, one extra large. I figured they'll work well as easy-to-rinse base layers for winter running too.