I think the main reason for the lack of advanced lesson is also the main reason why there are not so many good advanced textbooks in Japanese - the fact that there is a very small audience for these kind of materials.
Let's face it, people learn Japanese for a bunch of different reasons, and most language learners will drop out before reaching the more advanced levels of the language due to lack of time, motivation, etc...
So, it is natural that JapanesePod should focus on lower level learners. I am pretty certain they make up the majority of visitors to the site.
That said, increasing numbers of people are studying Japanese now, and the number of students approaching an advanced level out there must be growing. It would be nice if the site could offer some more focused lessons for those of us who choose to continue our studies at higher levels.
I think it would be really useful to have more of a business focus, for those of us trying to make some yen in the land of the rising sun. A good example of this kind of podcast for learners of English can be seen at
http://www.businessenglishpod.com/. Obviously, the ESL market is much larger than the Japanese learning market. But even a few more focused lessons in this area would be great - especially lessons focusing on keigo and business manners.
Maybe the site could find a retired Japanese businessperson with international experience (and a love of teaching) to co-host a ビジネス日本語 series. A long time foreign businessman in Japan like Terrie Lloyd
http://www.japaninc.com/about_terrie_lloyd would probably be a great host (or co-host) as well.
It would also be nice to have some more topical activities based around current issues in the news. Breaking News English (
http://www.breakingnewsenglish.com/ )does a good job of this for ESL learners. It would be really useful to have something like this in Japanese for learners at an advanced level.
Just a few ideas...
Keep up the good work.