I bought My original Z4 in 2006 (2003 model) for $15K, got a deal and sold it in 2012 for $11K, probably could have done better but wanted to move it
The price of new Z4's is very high. I decided to go the Certified route with one still under the original warranty and low miles and saved almost $20K. Cost me $35K for my 2009 and with 18 months of manufactured Wrranty, free maintenence followed by two years CPO, I am not concerned about issues. Had it 6 months and its been great.
The biggest depreciation is always the moment you drive it off the lot new and the first couple of years after that
2009 Z4 sDrive30i and a 2004 Toyota Land Cruiser - Lifted, locked and a few other toys