A.I. requires computational power. The game is already tapped out with the physics engine and rendering output.
More powerful hardware allows them to do much more - improved damage, improved sounds (this requires RAM/CPU), improved AI. Who knows, they might revamp the entire game. The issue is that PD currently have their priorities wrong.
From my lofty perch as an IT professional, with a pretty good understanding of how 'computational power' is used, let me tell you that the scripts they are currently using are equally 'complicated' to those that they could use to make the AI behave properly. They are using more variables now
The behaviour they have implemented at the moment is complex. It's just fucking stupid as well.
A very simple step in the right direction would be to have the AI travel at an appropriate, constant, racing speed that each car is capable of. This would mean that the player would only be involved in a constant 'race' situation if the variables outside of the game's control (driving prowess and car selection, to an extent, for open-class races) if those variables levelled out to equalling the lead car's pace. If you were too slow or too fast, you'd be just that. But it wouldn't vary wildly within a single race as it does now. That has always been the bedrock of the GT series.
What it could easily be (and has been in previous iterations):
Foot down all the way when on the throttle, break at given point, turn, back on gas, off you go.
What they currently have in GT6:
Foot down all the way when on the throttle, break at given point, turn, back on gas, off you go, continuously check for gap to human player, cross-check against total race-time remaining, based on values returned by numerous variables at any given point adjust driving speed of lead car by n%, go through variables cycle again over and over again until requisite gap is closed, then begin to consult same variables but with second table of outcomes which results in adjusting driving speed of second-placed (first AI) car by n% the other way.
Which of those two scripting descriptions sounds simpler and, thus, requires less 'computational power'?
The prosecution rests.