Reviving a long, unanswered thread. My state has similar rules allowing a 10+ year old car to be registered as a collector vehicle if <500 units were manufactured for USA distribution for all given production years. I reached out to BMW NA and received some generic language "does not share production numbers for obvious reasons."
The Z4M NA VIN database shows the following coupe breakdown
2005 - 2
2006 - 1137
2007 - 536
2008 - 140
TOTAL - 1815
https://web.archive.org/web/20160531...ion%20Info.csv
Unsure what the breakdown is for USA specifically, however 2006 disqualifies it in my state regardless.