We at LFO Club organise semi-random races.I'll get around to them all eventually..!
Most (almost all) of my racing is in a private MP lobby and we have been guilty of sticking to the same GT3 cars for far too long. We've only just discovered the unbridled joy that is DTM, for example...!
http://randomnumbergenerator.intemodino.com/es/generador-de-numeros-al-azar.html
That's all you need. You random a car, random a circuit, pick the layout that better fits the car and race. There're some times that you need to repick a circuit because you've got Road D@Bathurst lol But I garantee this thing is gold for discovering awesome combos and be surprised by cars you'd never expect to be so good.
Cars in red are our community's favorites.
Edit: For extra surprising experience we pick Real Weather and random the hour. Soooooooo goooood.