Oh I agree absolutely with most of your points. I like wayfinder as I now have one bit of kit which is portable. I appreciate TT etc now do Mp3 playback, but I cannot telnet or VNC into my myth box at home.
What I would really like to see are a link between carman, GPS and the internet so that a database of fuel stations and prices in say a 15 mile range along the route can be downloaded and displayed on the satnav with a choice of detours to either the nearest or the cheapest when the fuel reached a certain level - say a 1/4 tank.
Rather than full blown voice, simple voice tags for commands would be extremly useful, such as play, pause, next etc. Similar to the voice controlled dialing most phones have.
I have mobile broadband on my phone, so any internet based stuff is already possible. I have once used it to download a menu from may favorite indian takeaway so we could choose, and then phone an order to collect on the way home. A lot of this stuff is there already, but the bits just need putting together correctly.