F650GS vs. Wee
I own a 2008 DL650 ABS and I love my Wee...BUT I have also put about 2500 miles (each) on both the "old" (single cylinder 650 cc) and the "new" (twin cylinder 800cc) F650GS. The Wee is a much better road bike than the "old" F650, but the "new" F650GS is a pretty close match to the DL650. NOTE: If you are looking at used bikes for riding mostly on the road I would argue against the "old" F650GS in favor of the V-Strom. The decision between a V-Strom and the "new" (twin) F650GS is much less clear to me.
Plusses and minuses (in my opinion):
650 V-Strom: Plus= Smooth engine that pulls well for a 650, good (upright) ergonomics (I'm 5'9'' and 170#), fun to ride, good room for two-up riding, decent weather "coverage", lots of aftermarket stuff available to fix "issues."
Minus= "Issues" most people tackle: Seat, windscreen, lack of centerstand. "Issues" you live with: not the lightest bike, cross-winds can upset the handling, some people don't like the styling.
"New" F650GS: Plus= Nice power, remarkably smooth for a parallel twin, OK room for two-up riding, nice (upright) ergonomics (very simlar to the Wee), fun to ride. Wind in the face fun. Some people have a strong pro-BMW view.
Minus= Lack of weather "coverage", the BMW 800cc engine doen't have the long and positive track record of the Suzuki 650cc engine.
My thoughts are similar to the approach of "Buy one of them, ride it, if you don't like it....sell it and buy the other." The biggest difference is that the DL650 will give you more protection from bad weather, but you pay the price in that it feels a little heavier and is probably a little more sensative to cross-winds because it has a larger surface area when viewed from the side. Of course that larger surface is also what keeps the rain, etc. off of you. I think you'd be happy with either bike.