I'd recommend new tires (and if you can afford it, wider wheels). This allows for better traction in ALL conditions, which is what you should be concerned about more than power adders. Plus the fact that new tires (especially if you get wider wheels) can simply transform the handling of this car.
How old is your son and how long has he been driving? This will help with the decision process.
How old is your son and how long has he been driving? This will help with the decision process.