What were some of the changes they made from the 03 Z's to the 04 Z's?

 

i remember reading a thread about this earlier. use the search function and i'm sure you'll get the results you're lookin for.

 

https://my350z.com/forum/2003-2009-nissan-350z/149067-differences-between-2003-and-2004-a.html

 

Revised damping (more compliant ride with Euro tuned suspension)
Interior Changes including knee pads and some other stuff
Revised O2 sensor (wideband)

And the change was made at a half year meaning 2004.5 got the revisions.