The harder you drive a car, the more often it will break down. Period.
You add horsepower and torque, expect more things to break over time. You're exceeding the engineering original limits.
I believe Subarus are very well built, and can take some abuse, but in the end, every machine wears out and breaks down.
That's not to say your buddy can't autocross his car and still have it double as a DD, but he'll have to make some concessions and compromises, IMHO.