In terms of GPS units, it is a pretty ancient setup. I suspect it was pretty 'up to date' when it was released.
That said, when I have used it, it was pretty accurate.
Fortunately, I live where they use actual street numbers, so the post code problem is not so serious.
There is long thread on here regarding checking and upgrading the f/w. Updating the f/w is not for the faint of heart and even then I don't believe it will get you what you are looking for. Best to use a portable, TomTom, etc, or replace the head unit; for up to date GPS features.
I believe, ConnectNav+ has the color screen and ConnectNav is black and white. I am not what other features are different.