Before I write my ideas for new events I just want to define some terms...
"Road Cars" - That should be quite clear- cars that are not race cars....
"LM Cars" - Race cars based on a actual road car (like German Touring Cars, Supra Race Car, NSX Race Cars, Corvette Race Car, Viper Race Car etc.)
"Prototype" - Race Cars that are not based on a road car - like the cars that compete in the "like the wind" challenge.
And like it seems usual in GT that there is a car that is "out of class" in nearly every race - that should definitely not be the case in the races I suggest - because one should be able to compete with a car that falls in between the respective category...
"Prototype championship"
- Monza 15 Laps
- Circuit de la Sarte 5 Laps
- Fuji Speedway 15 Laps
- High Speed Ring 15 Laps
-Daytona Road Course 15 Laps
- Indianapolis Road Course 15 Laps
- Nürburgring (GP + Nordschleife combined) (4 Laps)
"Road Cars vs. Race Cars"
Race Cars should be different "RM" Cars
- Nürburgring (GP + Nordschleife) 2 Laps
- Special Stage Rout 5 12 Laps
- Laguna Seca 10 Laps
- Grand Valley 8 Laps
- Cape Ring 6 Laps
Japan vs. US
"RM" cars
- Daytona (Road) 10 Laps
- Indy (Road) 10 Laps
- Laguna Seca 10 Laps
- Suzuka 10 Laps
- Tokio 246 10 Laps
- Fuji 10 Laps
Europe vs. US
Road Cars
- Monza 10 Laps
- Circuit de la Sarte 10 Laps
- Eiger Nordwand (Road) 10 Laps
- Indy (Road) 10 Laps
- Laguna Seca 10 Laps
- Nürburgring (GP) 10 Laps
- Circuti de la Sarte 4 Laps
Europe vs. Japan
Road Cars
- Nürburgring Nordschleife 3 Laps
- Top Gear Test Track 10 Laps
- London 10 Laps
-Special Stage Rout 5 10 Laps
- Suzuka 10 Laps
- Fuji 10 Laps
Also the "Not Tuned Cars" Event from GT4 was nice - but I am not certain if this would be a good idea for GT5 as you can't redo a lot of tuning options... So you would need a second one of the car if you already did this tuning....
All the events I suggested should be championship events and should pay out multiple (different) price cars. So there is more motivation to redo the event

In the case of the "Road cars vs. RM cars" event it should be associated with the type of car you use for the event.