We stayed in 6192 on the Dream last summer and I never noticed any fumes or soot on our 4 day cruise, and we were out there often. We napped out there a lot, too, and I am very sensitive to odors. I did notice (smell) someone 2 verandahs over that was smoking a cigar, but I'm guessing he got caught because it only happened the one time.
I would pay extra for the aft verandah staterooms, but I'm glad I don't have to. The size of the verandah almost doubled the size of the room, and the reclining chairs out there were awesome. I also liked how most of the verandah was covered, so we could sit out there in the rain without worrying about getting wet (and the sun without putting on sunscreen).