The 323 didn't come stock with the computer (tells avg mileage, avg speed, etc). That came stock later. Other than that, there's really not much difference. Foglights became standard somewhere along the line. 328s had those minor things I believe. All 3 series came pretty stripped. Moonroof, leather, xenons. All those things were options I believe. No real big significant changes.
The main interior features that separated them were the headlight surround is a different color, there are silver rings around the guages, and the e-brake lever is leather. That's the diff btw a 330 and a 325. I imagine it's the same on the 328 vs 323. Nothing major. Biggest diff btw the two cars is just the rims and the engine.