If his price for the Tenere is good at $8,500, and you're willing to go as low as $13K, that'd mean a $4,500 valuation on the Valk.
Hard to say since I don't know mileage and condition, but it looks pretty nice. Check out cycletrader. RARELY will an Interstate be listed as low as $4,500, even with 70 or 80K miles. You might have to wait a bit, but I'd be willing to bet you'd get at least that out of it, and maybe more.
I'm listed on that website at $14K... I'd rather someone here get it if I'm taking less, but it's been up for a few months now without much interest.
It's just bad timing on a Goldwing I guess... with the "new" model coming out soon.
$8.5K for the 2012 is a bit steep... but he does have low mileage and the high $$$ luggage on it (along with a few other pricey options). With the extras, $8.5K isn't a bad price.
Of course, in the end, I may keep the Valk instead... it's a bit much for what I need the bike to be right now, but I do love the Flat 6.