I don't know how you can be bored with GT5, it has almost everything that GT4 has, and a whole lot more.
You must be fishing for more things you can do with GT5, if so, try this:
Go to arcade mode and choose 'single race', equip your car with comfort tires or remove some mods BEFORE THE RACE LOADS. When the race is loaded, restore your racing tires or choose your previously removed mods. The AI field of racers chosen, will have comfort tires or less horsepower etc.
Now start the race. 3...2...1...When the race starts, don't race, instead, hit the brakes, let the seconds tick off and give your competition a 'head start'. Now see if you can overcome the delayed start. If you win by 10 seconds, add 10 seconds to your delayed start and race again.
I like to do 3 laps of the ring this way, it can be quite exciting as you are on the 3rd lap and closing in on your competition. Will you be able to do it? Will it be a 'photo finish'? The possibilities are endless.
I always get a laugh when I beat Lambo's, Vette's and Viper's with a Pick up truck or a Honda Odyssey. It can also be some awesome videos. Who doesn't like a 'photo finish', 'come from behind', or a 'underdog' win?
Anyone want to add to this ???