A GS Guzzi wouldn't be practical: One of the great things about the BMW flat twin is when you get down a trail were either space or trail conditions won't allow you to turn the pig around you can DROP it on one cyclinder and spin it around!
Of course, then you need a couple of buddies to help you pick it back up again. (this is true by the way - a method many AdvRiders employ!)
I think Guzzi could take some cues from BMW however: Look at thier line-up, they aren't trying to compete with Ducati, Aprilla, Honda. They're creating new markets!!
Everyone here is complaining about the "old" Guzzi V-Twin. Look at the range BMW has with the "old" Flat twin: R1100S R1150R R1200RT R1200ST R1150GSADV R1200GS and all the C1200 cruisers.
jb