04 -> 05:
http://features.evolutionm.net/newsitem/75
Not sure about 03 -> 04
Good things about the 05:
- some changes to the tranny allegedly make it shift smoother
- 10.5 cm turbo hotside (this is one of the common aftermarket upgrades)
- finally a front limited slip diff and electronic active centre diff.
Bad things about the 05:
- a lot less options than before. For example, HID headlights were standard on 03s, an option on 04s, now on 05s the only way to get them is to get the sun, sound + leather package (3k+).
- No more intercooler sprayer.
- Rev limiter at 5000 rpm with the car in gear and the clutch in (supposedly can be removed with a reflash)
No US evo has active yaw control yet, but there are strong rumours that the evo 9, due out this year, will have it, along with the spanky bilstein suspension and 6 speed from the evo MR (drool)
Check this vid of the evo 9 ... it appears that they have finally fixed the crappy turning circle!
link
I am secretly hoping that 06 will be the year of the evo 9 vs the spec c STi here in the US. Assuming subaru doesn't gay up the body of the STi like some of the early photoshops suggest. And that I win the lottery.
I think the biggest thing about buying a used evo vs buying a new one will be the front LSD, and you can get that (along with any parts from TSBs) added to older evos. This place has a good rep on evom:
linky mclink