Richard
You will find the limitation on the Sat Nav is the coverage of the map CD ... the coverage is near complete in most urban areas but much more limited in rural areas with the exception of major highways
Having done Kangaroo valley before the drive day this was not unexpected on my part, but I would guess this was your first trip in the MINI to a more remote location ... the GPS component still functions correctly just has no data to plot against, if you have the right map book you could use the long & lat to plot your own position
My understanding of Map CDs is that they are made by independent companies but would need to be supported by the underlying Sat Nav firmware in order to operate ... also you want a new Map CD you pay for it
I think Tim (IML337) was quoted something in the order of $300-400 for this, but don't quote me
You can always scroll the map to where you are going ahead of time and check out the degree of coverage (recommend scrolling initially with low resolution scale 100km and then refine the resolution when you get to your area of interest) ... I have used this method for example to check what degree of coverage I can expect for our little tour down to Tassie in May of next year
On drive days given that some of the roads we are taking are not exactly main highway I would generally recommend following someone unless you are very clear where we are going ... the Sat Nav is a great aid but it isn't bullet proof ...
Cheers
Steve