'02-'05 are essentially the same, except that in mid '05 they started the first facelift. So '05 Z33 are harder to differentiate for the newcomers.
The first facelift has:
- new front bumper (different lip, side reflector)
- new front HID lights
- LED tail lights
- different interior (without electric heated seat button on your elbows and other minor stuff)
- slightly better interior quality, less hard plastics
- new 5 spoke rims
- 300bhp VQ35DE Rev-Up engine for 6MT (7,000 RPM rev-limit instead of 6,500 RPM)
Late '05 to '06 has these stuff above and is worth more than the first '02 to '05 batch.
In '07, they started second facelift. This time exterior changes only to the hood and also new rims (18" front 19" rear) for ST version. It has new engine, the VQ35HR, which has 7,500 RPM rev limit and a lot of new engine components like dual-intake. '07-'08 models have this new VQ35HR for both manual and auto models.
The trims available are:
Version T : Luxury trim, leather, heated seat, GPS navigation, BOSE.
Version S : Sports trim, Brembo, VDC
Version ST : Grand Tourer trim, has features of Sports + Luxury trim.
So ST trims are usually the more expensive ones with more features. If you see Ver T or Ver S priced along ST, that is usually a possibility of it being overpriced.