When I first got my 02 640 Adventure, one of the first trips I went on was a Baja ride with some pretty good (as in motocross racer type) riders. I certainly wasn't as skilled as they were, but we were all amazed at the capabilities of my bike in the dirt. What a blast!
A few months ago, I decided to get a set of street wheels/tires as well. So, I installed a pair of 17" wheels with sticky rubber (complete with rotor, sprocket, etc.), a pumper carb properly jetted, a bar snake and some soft grips, some bar risers, a Scotts dampener, and maybe best of all....a Bill Mayer saddle.
I must say....the transformation is startling! The bike feels like a canyon racer now. I can easily do hundreds of miles a day without strain. The vibration has been minimized, and is a non factor now.
There was a time when I thought I might trade up for a 950 Adventure and keep the 640 in dirt mode, but I no longer want a 950 'cause I'm having too much damn fun on the 640!
Two sets of wheels for your 640 Adventure, and you have a bike with a serious multiple personality disorder!