Sorry for this 'wall of text'
@OP
I really like the concept. Its not the racing against the AI that erks me, its the fact that you have to race against only the AI to make a decent amount of money over a certain period of time (AKA grinding), as you make next to nothing for online racing. Take the seasonals for example. You make millions grinding a single event for hours, but do you have fun doing it? No. Why does every single racing game I have ever played get to the point of grinding for hours upon hours, just to get that awesome expensive car. If you take a look back at it, this is what ultimately makes racing games get boring and repetitive. After grinding a few hours, you get into the state of mind that the driving part, the part that was intended to be the fun part of the game has turned into a chore, and the fun part of the game is now the relief of being done grinding and now you have a new car.
Here is my idea: Replace seasonals with what I call "Weekly Focus Races." Here is how it works: When you hold online races with a certain car type or performance level you will make 1000% of the normal payout for online at the end of the race, but for that week only. The regulations change every week. Of course the regulations for these races would be decided by Polyphony. This will increase the competitive edge online so people will race for money, not just pride. It would also increase the different types of racing done in GT5 online, which will help with the problem of not having enough diversity in the cars people have in their garages. Another advantage to this would be an improved ranking system, in which new players strive to be better all around racers and struggle to make money at first, but after playing the game they will improve, make more money, and ultimately have fun playing Gran Turismo.
If you don't understand my idea, here is an example:
PD's message to all of GT6's players: This week's Focus races are GT500 races, 500 PP races, LMP races, and 600 PP races. In each of these races you will recieve 1000% the normal payout for completing this race.
*User clicks the "Focus race" button on the menu and is directed to another menu that looks like seasonals, but instead has a list of that week's focus races. He clicks on one of them and is directed to a list of user made lobbies that are restricted to that car type/performance level. He will have the choice to either make a new lobby that has in which he can not change the car restrictions, but can change other regulations such as driving aids, track selection and such, or he can join an existing room.
Although I would not like to take the single player out of GT, I believe it could play a minimal part in GT just like it does in Call of Duty.
Really, I have millions of ideas. I could go on for hours.