I don't recall the GT series having nerfed AI. Unlike Ridge Racer, Daytona, or even a game like Mario Kart where the AI will increase or decrease in difficulty depending on the player's ability.
It's "The Real Driving Simulator" after all.
Just get it NegroD! New for the series: Online racing, weather effects, damage modeling, enviromental modeling, 70+ tracks and over 900 cars...! I'd say to be cautious if it was a new series, but I think for a console game GT has stood the test of time.
IMHO $60 is not much for a game I'm as sure as I can be that a couple years from now I'll still enjoy playing. As far as new releases are concerned, it's not even a game I'm having a moments hesitation in deciding to buy/not buy.:clappy
Like Nike says...