Well, yes, there's not that much diff between the GS and the ADV. The suspension of the ADV is 2cm higher, slightly upgraded, the windshield is a bit wider, protects you better, the tank takes 10 L more, it is slightly heavier. All in all no significant difference.
IMHO the 1150 is still the more reliable bike, esp. regarding the electronics. But the 1200 is a lot lighter and ergo easier to handle.
Only when we pause to wonder
do we go beyond the limits of our little lives.