As the director of a 500+ runner race, an officer in a club that organizes 25 low-key, low-fee races per year, that holds about 100 training runs per year and weekly track workouts in 3 different locations, I can truly say that without the AARC and RRCA, we would not be able to afford to serve so many runners.
Even if the only purpose of the AARC/RRCA was to provide insurance for running clubs, they would still be an incredible asset for runners. We could not afford to purchase insurance on our own for the big race, smaller races, and all our training runs and track workouts. For less than $500 we are covered. If we had to purchase coverage on our own directly through an insurance company we would be paying 10 times that.
As to the note from 'IRS' above, I think you are all wet. I have 20+ years in the tax field and am confident that the AARC/RRCA's group exemptions are valid for member clubs.
This is a great secondary benefit for our club as it allows us to accept tax deductible donations so that we can support youth runners in our area who cannot otherwise afford to travel to races.