Having a CarPC longterm requires a certain drive, pardon the pun. Either you have it or you don't. If you truly believe that a phone will do everything you need, then you probably don't have that drive.
That being said, you can get an HD radio (which picks up normal stations) for $50, though the LCD screen issue would be more expensive to fix as a transflective is $600+.
As for maps, I have no idea what supports Australia.
Whatever you do, do NOT upgrade your Roadrunner to riderunner. You'll be forced to upgrade every 4(?) someodd months afterward so you can't ever get it set up how you like it without something breaking.