Very informative thread!
I wasn't aware about the mass production in 2007. So it seems like will be easiest to find decent 2007 MY on the market in the 2010-2011 timeframe.
I did a quick search on autotrader to provide some stats on US based 2006-2007 Z4MC under $30k.
23 were found: 6 were 2006 MY, 16 were 2007 MY, 1 was 2008 MY. This is in line with the production patterns stated in previous post. I read on one of the ads that only 248 M coupes were brought to the US in 2008.