I agree that the KZ is a cool looking bike and that it is way sportier than a GS. And so does the rest of europe therefore a KZ bike in a reasonable condition is much much more expensive than a GS. And most of them have had a tough life as being a sportsbike. The GS has always been more of a touring bike and therefore it's life has been more lay-back.
And all old Kawa 4 cilinders sound as if they're about to break down. They rattle and hiss like a can full of gravel shaking up and down.