I had iDrive (navigation) on my 335i and I don't have iDrive on my Z4. It's definitely cool and easy to use, but I don't miss it that much. Google Navigation on my smart phone is superior than the iDrive nav, but the built-in navigation has the ease of use factor. Now when I need navigation, I just take my compact windshield mount out of the center storage (where the screen would have been), and put my phone up. I would say if the car has it, wonderful. If not, it's not a deal breaker.
If I'm not mistaken, Bluetooth is not standard until 2012. In 2011, if you want Bluetooth, you'll need to have either the standalone BMW Assist package, or the Premium Package, which includes BMW Assist.
2009 Z4 sDrive35i DCT, AW/CR
2010 335i Coupe 6MT, SG/CR [SOLD]