Tom, here is what little I know and I hope it helps.
First off, opinions on tires vary drastically, especially with the Goldwing. You have to keep in mind that the Goldwing has a wide variety and spans a broad age of riders.
There are very "Spirited" riders, conservative riders, down right hardcore riders and then there are riders who seldom get the bike to lean any more than 5 degrees.
With that being said, those who get 12,000 plus miles on a set of any motorcycle tire are in the group who ride conservatively, ride a lot of flat straight road and seldom get crazy in the twisties.
Now I know there will be people jump all over me and tell me they got xx,xxx miles on their tires and they claim to ride aggressively. All I can tell you is, one mans definition of "Riding aggressive" can and is very different from the next mans.
And this is fine, it's all about having fun riding. I could care less how anyone rides his or her bike. The point is tom, you can NOT listen to the masses on a Goldwing site and get any real data on what to expect from your tires.
Me my self, I just mounted a set of Bridgestones on my 08' Monday. I bought the bike new in May this year with the stock dunlops on it. I had right at 6300 miles on them and they were getting too loud for my taste. They still have over 1/3 tread life left on them and I imagine I could have squeezed another couple thousand miles from them.
But these are the same tires I see other people claim they got 12k or better out of and say they still had tread left?
Sorry, I don't buy it unless you never break the speed limit and you start breaking 1/4 mile before your stop!
If you get 9k miles out of a MC tire, I say that is about right. As for me, I am sure I will be changing these out at around 7k -8k due to the way I ride. I am HARD on breaks and even harder on the throttle from the stop lights. I constantly push the limits of my abilities in the twisties too. But the fact is, most of my riding is in Southeast Texas on flat roads and I ride my wing as a daily driver to and from work. The D250 I took off the rear was shaped more like a car tire than a MC tire after 6300 miles due to all the highway riding I do. I expect the Stones to do about the same but with better grip and little to no cupping.
Take it for what it's worth but do not base your opinion of what to expect from your tires based on what you read on a forum. Use your own judgment and stick with what works for you.