I read on edmunds that the 2004+ have over two thousand new parts over the 2003 versions.
Go for a 2004+ not just cause of the face lift but because of at least these:
More HP 
Xdrive
Panoramic sunroof
6 gears instead of 5
Angel Eyes (see below)
Adaptive Xenon (they turn with your steering wheel)
Valvetronic (4.4i is more fuel efficient than 3.0i)
BMW Assist with GPS
MP3 CD player Ipod adapter