Have got the 04 M1000sie (2 weeks ago), and the only change there is from the 03 is the mirrors, which are the S4R type (I think ???) and not the 'mickey ones'.
Traffic slipper clutch (not a full competition one) is now being fitted to the 620 & 800 this year, but havent heard it is going onto the 1000.... yet.....
ps- weather has been so slippy/wet/frosty in good old blighty, I havent had much chance to get some mileage in yet :'(
AFAIK, the slipper clutch is only on the 620, and it was the only significant change to the air-cooled Monsters in '04. If I am right, the only difference you'll notice on the M1000 is the mirrors. If you get a good price on an '03, or can take advantage of the financing deal on the '03s, then go for it.