1) New 3 series is set to release in mid-05, but i doubt the value will decrease on the E46, the new 3 series is an ugly child....
2) The 2001 3 series front bumper is of a different design than its children, 2002 on.
3) The 2004 3 series has a little slicker looking front end, created by altering the look of the corner lights. The 2004 also features a little difference in package options, as you can get teh AWD, M Sport, etc....
4) If you have the money, i would suggest ordering an 04 or an early 05, that way you get all the features you want, instead of hunting for a used bimmer with them.