Engine changes? Interior changes? Exterior changes? Any changes? Thanks!

Everything stated above as well as 1/2 in wider wheels in 05, inside of the head lights were a little darker in 05, and stereo was an option in 04 then became standard in 05.

The best place to look is edmunds.com and compare the two cars. However, at this moment, l cannot get into the edmunds but rather able to do it in cars.com

Engine still output the similar bhps. Interior you may able to get something upgrade in 2005 model.

l think the best way to answer your question is go to the dealer and ask for their packages.

Also on a mechanical note the wheel bearings are bettter in the 05's

The main difference is tht the steering wheel is different.
The 2004 had a 4 spoke steering wheel, while the 2005 had a 3 spoke steering wheel.

The 2005 model also had some extra options like more paint colors and more interior colors.

In body, looks, comfort, and powertrain, they are exactly the same.

If you're thinking about getting an 04 or 05 STi.
just get the '05.
Better wheel bearings, wider wheels, new helical LSD in front, interior center console upgrade that looks way better, standard audio system, nicer steering wheel.. and some other stuff l can not remember