Well, i never thought of them as "imposing," but now that I step back from it, the deep shells and raw finish do give them an imposing attitude.
I would have actually preferred a 20 inch bass drum, but those are extremely hard to get, even by Spirit Drum standards. The logs must be 22 inches, which means they literally weigh tons if you can find them. But even the 18 inch drum sounds resonant, thick and punchy.
You are perceptive to notice how the Fiberskyns add to the persona of the set. The shells and lug style give it a primitive quality and the Fiberskyns accentuate that.
You are right about the sound - it is thunderous. It dominates the entire house and I have to be careful when I play; ideally, when no one else is home.
The shells with RIMS hardware in total weigh around 100 pounds for the set of six drums. Add in the DW 9000 series stands and it's a workout to move. I like to lift heavy objects, however, and I need to lose weight more than the drums do.