As above the last run of classics (Version 6) were 1999-2000. They had much nicer interiors with better seats, momo steering wheel, nicer less plasticy inside. There was a small increase in power (not very much more but every little counts). The front brakes were four pot calipers like the STI rather then the previous two pot. The lights are crystal clear rather then frosted which makes the car look a bit more modern.
As for newer cars, the advantages I can see are a slightly more comfortable ride, less noise, modern looks, more modern interior which looks less dated, stiffer chassis. Power is the same and I think the newer cars are heavier and have a bit less sensation of speed.
As has already been said, unmodified cars are out there. I live near a beautifull Mica blue which is 100% standard from the 10 years ago it rolled out of the factory. Mine was also standard 4 years ago when I brought it. Don't compromise be picky.