Remember, raly cars are driven on the road and have a full cage, Helmets are not worn on road sections or whilst travelling to and from the start/finish.
My cage is fully padded.
The biggest problems with a cage are the loss of the rear seats which makes the Mini a 2-seat car, the possible increase in insurance unless it is a historic competition car and the inconvenience of the necessary full-harness belts.
If someone is nervous about driving a Mini or any other older-generation car in modern traffic, the the best advice is not to do so. I am not being sarcastic here, just pragmatic. If I was nervous about doing something, I probably would not do it. A Mini is expensive to own and run compared with a modern small car and the modern has all the safety stuff, like enhanced body strength, dual-braking system, crash-resistant bumpers, ABS, good de-misting, big brakes, longer-travel suspension, etc.