Dunno about tracks down there, I know hundreds this side of Melbourne though. As for servicing Nissan and most other manufacturers only recommend 5000 for high use engines, I'm fairly sure there is something in the manual about what they consider high use but for the majority of people 10K is adequate and wont hamper your warranties or anything.
There are plenty of people who subscribe to the 5K theory and that's fine for them but unless you fit into the high use category or you really want to I wouldn't be too worried about staying at 10K.
They are obviously different engines but we've always run UD, Mitsu and Isuzu engines in the 8 and 11 tonners for atleast 15k between services and never had any problems. On the other end of the scale a mate of mine ran his Prado for more than 120K and only had the 1000K tighten done, car never missed a beat in 18 months and the price that took off on the trade in on the new Prado was less than it would have cost him for factory servicing over those 120K. I wouldn't suggest either idea is good for the Nav but I reckon 10K is fine.