Hi Trader,
I think I understand what you are saying, and it was difficult for me to get a good grasp of it at first, too. But I have added some screenshots to try to help explain.
You are probably correct that, for the most part, American companies using adsense and other online ppc advertising do not value foreign traffic highly, because - depending on the good or service, of course - they may not be able to convert that traffic into customers. However, it is the same way for foreign companies - they do not necessarily want American traffic.
Here is a screen shot of my site, MacauHôtels.com, in English:
Of course you see the English adsense ads.
Now, here is my site after clicking on the Japanese flag under the header to tranlate it to Japanese:
See how the adsense changes to serve Japanese ads?
This is the same thing that parking providers like Namedrive offer: native language ads and templates to maximize your CTR and revenue.
So, with highly-searched-for terms in other languages, paying the same as (or sometimes higher than) top ASCII keywords, and optimized or developed, the potential is there for a lot of money to be made, same as any other top domain.
I hope this helps a bit. I'm not trying to convince you one way or the other about investing in IDNs, just trying to answer your questions and continue the discussion.