Not at the moment because I don't really need it, but I wired a 5m usb cable all the way to the trunk as well exactly for that purpose. If I do decide to install something, I would probably go for a BU 353 S4 GPS receiver and RouteBuddy as software
first your car is awesome...loved.....I'm apple lover I have mac mini as movie server at my house but I ended up installing a 8" tablet on my suv....What I did And I recommend you is , I did on my mac mini add RAm like 8gb dont know how much you have but the main thing which will turn your computer 5x faster the boot and the use is switch the hard drive for a SSD hard drive It's solid hard drive this is my mac mini http://www.youtube.com/watch?v=i159OCX79OE
another ideia is for the backup camera install a realy to receive the signal from the + from the reverse and switch the screen , so when you put on reverse automatic goes on reverse..
I had problem do to the amp on mine I almost did what you did like putting 4 outputs adapter, but went to best buy and bought a media receiver from jvc for $99 and it comes with bluetooth, so It will amp the sound from a jack input and add a bluetooth at the same time
here is the video os my project took me 2 weeks and still working on it...It reads my 2T hard drive with bluray movies that I downloaded from internet ....next project is install a 20" screen led tv on sunroof with hdmi....