firstly is your Z brand new or second hand and how many miles has it done.
You should still have warranty on the Z so steering rack, boot struts, stereo and oxygen sensors should be covered.
Clutch sound very iffy, I would be arguing that one but it is down to driving style and a difficult one to proove.
Did you test drive the other 350z, Ihave to say I've not noticed any vibration on mine. Try another dealer and test drive there Z's for the same issue.