When it comes to iPod's, you have to think about one question:
What time of year will Apple sell the most iPod's?
The answer is....Christmas!
If they release a new iPod in September, by the time December rolls around the new iPod would be 3 months old. Ancient in terms of technology.
I'd say, look for an iPod special event between October 15 and November 1, just in time for the holiday shopping season.