The AVIC is a very slick system, my brother has it in his Lexus IS. However, you're in the same boat as me. You can add the AVIC, but you won't have a stock look and the steering wheel controls will NOT work. In addition, if you car is still under warranty, aftermarket electronics is a good way for the dealer to blame it/you for any problems.

My suggestion is to get a portable GPS unit, like Garmin StreetPilot. You can use it any car and its actually better IMO than the OEM NAV (its touchscreen) and more intuitive. The best part is that it'll run less than $1K!