I'm not concerned with drag and think it's a silly thing to worry about, unless you're on a track. There's a lot more to be concerned with on the road than drag.
As for how it looks, your statement is sillier than any top case could ever look. I don't mind the look, but I am not into it.
What are you carrying around everyday that you need a duffle bag for? I transport my laptop, in a sleeve, along with my tool roll, everyday to work. Any time I go on longer rides, I can fit water/snacks in there and not have to worry about carrying it on my back. For most weekend trips, I can fit everything I need in my top case. A couple pairs of boxers, couple pairs of socks and a couple shirts. I don't run side cases because I commute and split everyday. But on longer rides they'd be able to carry camping gear and more than enough clothing/gear.