I'm actually starting to lean towards doing an aftermarket head like this
Alpine It has bluetooth, iPhone & Siri integration. You can set the color to BMW amber, and even control it from the steering wheel. It will be a lot less than adding the amp interface and Media bridge. Probably will function lot better. The only real downside I can see is the looks of the thing. I'm also unsure how you could assess the car computer functions without the stock deck.