The versys has more power and gets better gas mileage. But the fact that you have farkled your 2008 KLR means you like to work on your own stuff. the versys doesn't lend itself to that. Also the insurance is much higher on a twin sport bike than it is on a dual sport single. The versys also had an upgrade to rubber engine mounts in recent years, but I am not sure why. But the main reason that you should keep your KLR is that it is a babe magnet! So you may go farther in less time, but you will lose out on the LaDies!
If you do decide to go with the versys
low ball him. He can't unload the versys that is why he is willing to make a deal, so start at a straight trade and work from there.