EDIT - Thanks to BrandonD93 (and now myself) it has now been confirmed that additional events are unlocked after completing all 6 championships. You may want to consider this before spending a wad of cash on a supercar rather than a large case.
There are a total of 5 extra events including an endurance race
This appears to be glitched at the moment as I have fully completed all series and showcases in the championship and it didn't pop. Nobody else has it either so I think it's safe to say it's borked.