I echo sgould's comments, having Hirsched my 2.3t 9-5, both engine and suspension. The upgrade for the 9-3 1.8t is probably the best value across the Hirsch range. Factor in an increase in insurance, many will run away from you with a tuned car - get some info from your insurers first. But that aside, if you get it done, you won't regret it, and IMHO a Hirsched 1.8t is (s)miles better than a 2.0t. I had a 2.0t 9-3 for 6 months before getting the 9-5.
Forget the official price, dealers should be desparate for this kind of business. Get a few quotes by phoning round. Factor in the price of petrol getting to a dealer some distance away if they're cheap. The process takes around an hour. The dealer downloads the software from Hirsch, and uploads it to your car. Money for old rope from the dealer's viewpoint.
Go for it!