This is a tough call. When this happened to me I retained the car and used the insurance proceeds to pay off the loan on it and the remainder on a vacation to puerto vallarta (I was 18, no regrets!). I drove the car for another 5 years and 100k or 120k miles. I finally got rid of it when i rear-ended a cop (I knew the cop, it was a small town). I collected a second insurance check and used it and the remainder of the car for a $3000 push/pull/drag trade in deal on a new-to-me Honda.
So I guess my advice is to keep it if its reliable for you and meets your needs. In other words, would you sell the car now irregardless of the hail damage? One big thing to consider, can you get a "better" car than the WRX with the $7k insurance proceeds (lower miles, newer/safer model, better mpg, whatever your criteria are)?