On my Dolphin I spent a lot of time chasing creaks and rattles. Yes, most were plastic on plastic, which I fixed by putting pieces of index card stock between places where two pieces of plastic come together around the windshield and overhead console area. My power visors also rattle when fully closed, so I just let them hang down about an inch.
My W-22 Dolphin always rode relatively well, but I drove a W-22 Winnebago once that seemed much rougher and noisier than my Dolphin and I can't really tell you why. This is before I started adding suspension goodies like Sumos to my coach, and I think all W-22 used the same springs, so it must really just come down to shocks and tires (and/or pressures). 80-85 lbs is where my Dolphin rides good and I can sense it riding a bit rougher as the tires heat up. I usually end up around 100 psi as they get up to temp.
Think of the Sumos as bigger, softer bump stops than the stock ones. They can cushion the blows a bit better and more progressively, but don't do a lot to smooth the ride otherwise.
I have Bilsteins too. No complaints from me about them, but there are those who swear by the oil-based Konis, so they might be worth trying.
2004 National Dolphin LX 6320, W-22, 8.1, Allison 1000, Front/rear "Trac" Bars & Anti-sway Bars, Sumo Springs, Roadmaster Reflex Steering Stabilizer, 2005 PT Cruiser Toad