Low traffic is good and the dome design is really incredible. It sounds to me like this is the rug you can both like :)
I would see how much space there is for negotiating, just feel out the situation.
Retail I would think 5000-7500 perhaps. This rug in particular may be at the lower end of the range. Kashmiri rugs specificially would need to be seen in person as construction, density, and many other factors weight heavily on value.
I would like to get some other opinions. I get the feeling there's probably a fair amount of room.
As for the investment: Persian or Indian... Indian rugs don't have the clout that Persian rugs do. Most Qum rugs will be at a higher price point for a 6x9 in comparable quality, design and colors. They are out there, but if you have your mind set on something, it's sometimes very hard to find similar. Unless you're willing to hunt for a long time and potentially pass this rug up, I would see how far you could negotiate this one down. Although some Persian rugs may generally "retain value" better, who's to say the monetary difference will be more rewarding than settling on a less than 'perfect' rug?
What I can say is Qum prices have gone up in the last few years, many people are concerned with the present situations perhaps making these rugs more difficult to attain. It's all guess.
Bottom line, I'd see how far you can work the price of this rug down. you're there and potentially ready to purchase. But not unless it's on your terms and you are happy. He's got an expensive rug, it's one of the most difficult objects to sell right now in the present climate. It's in his best interest to give you a good deal.