Hard side is not necessarily heavier than a soft-side. A better quality camper however is heavier than a cheaply made camper. Most Outfitters outweigh my hard side Lance 815. Yes, the Outfitter is a better quality camper over my Lance Lite.
An extended cab-over (N-S bed) soft side will probably allow the same mpg as a short nose (E-W bed) hard side.
I too travel the mountains and explore a lot of forest roads in NC, VA, TN, KY, and WV. I have yet to be blocked by limbs that a soft side would have been able to make it by. Yes, I have brushed a lot of limbs, but none have done damage.
One of the things my wife has fallen in love with traveling with the TC is always having everything with us all of the time. Being able to turn around on a dime is another big advantage.
But you can figure on just about doubling you fuel cost if you are getting 20 with the Subaru. So far I'm seeing about 11 mpg average.