I have been thinking about such an event for quite a while as well and my idea is that it should be about the "together" part more than about the golf. Sure, there will be great golf, there always is with GCA people involved. The quality of the golf is the least worry I have in this matter.
My idea is a GCA cruise. How about renting a sailboat or even a yacht and do some island/coastal hopping. We could play links golf during the day and then cruise to the next destination. Everyone would be together on the boat. Obviously, Scotland comes to mind with Arran, Kintyre, Islay, Jura, the Hebrides etc. But there are many locations where this would work golf-wise.
Yes, this is probably expensive and a dream. But the thread says "Ultimate GCA Event", so going to St Andrews seems a bit ordinary
Ulrich