Thats all good.
But what happen when someone smashes into you, and the refuses to pay up. if you only have 3rd party your insurance company will not act on your behalf. Therefore you have to chase up the person who hit you. and in most cases if the person refuses the only cause of action you have is to get a lawer and sue.
This is NOT CHEAP and required YOU to do all the work, you have to get quotes on the repairs, you have to pay for all the towing cost. and you are out of pocket till the person pays up. And then in the end if the person has no money and assets; you basically get nothing or get $10 a month for the rest of their life.
There is a reason why your full cover cost what it does.
JUST CARS are fair; i know of an r33 who had an accident front was completly gone; was declare a write-off; excesses was paid and they pay out. (owner was at fault) car was far from stock (400hp+)