Event Generator. We all seem to be calling out for this feature more and more these days. Hopefully it reaches a crescendo soon. It was implemented in GT2, and the time has come for it to return.
If I can add to this discussion I would say
we need this to be in A-Spec mode, with ALL of the possible Arcade and Online options (A.I. Difficulty, Tire Wear/Fuel Depletion, Tire Grip Low/Real, Damage off/low/high, Slipstream adjust, am i forgetting any?).
Arcade is nice to have- but ONLY because we don't have such options in A-spec. Period. We need to be
gaining xp,
earning cash, and
logging miles/wins while competing in our created championships. On top of that- based on the difficulty and size of your created event, maybe we could receive a gift car ticket for a triumphant win.

Level 1 tickets for single, low-stress races. High-difficulty, 20-race championships against higher-pp opponents should net you a level 20 ticket, or something along those lines. I would surely need a new PS3 within weeks. lol
One more important point, when selecting the opponents and their vehicles there should be a couple critical options. The first,
when selecting each opponent car- we should be able to choose the tires. This gives us a clean way to tighten the field AND strengthen the field overall. Example:
Give your top opponent cars Racing Hards, the lower-pp opponent cars could get Racing Softs, and give YOUR car Sports Mediums. This would make for some TOUGH racing. (If you like that sort of thing. And of course you could do just the opposite if you feel so inclined- but hopefully if you ride on Racing Softs and put all of the A.I. on Comfort Mediums then your prize ticket level drops drastically.)
.
As for the field of A.I. drivers- how about a simple slider called 'Field Disparity'?
All Easy______Mostly Easy______Balanced______Mostly Hard______All Hard
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^ I have chosen a setting between Mostly Hard and All Hard, and ideally that would pit me against a majority of level-10 opponents, with a couple of lower-level guys (5--9) spread about the field, just for fun.
Kaaaaazzzzzz-unori. Kazunori. Kazunori. We call out to youuuuuu.