I want to find out when special features like damage, better AI, weather effects etc gets unlocked in GT5, but the searches I performed just turned up guesses or rumours. Is there a definitive answer for how GT5 unlocks work?
I believe there is no "unlock" for features. Damage is in, and can be turned on in some modes. Weather effects appear in certain races (marked "change weather/time" in selections). Some higher level and special races have rules like no skid recovery, but no new magic will appear otherwise.
Software updates constantly provide more features, of course.
I know that the various race types in a-spec mode are unlocked when you reach certain levels.
The extreme series is at lv25 if I recall, and the super red bull challenge thing is at lv30.
There is a fuller list of unlocks over here, http://www.cheatcc.com/ps3/granturismo5cheatscodes.html