The two are as follows:
1. 2003 with 9 000km - price $4 000 USD (converted from NZD)
2. 2006 with 20 000km - price $6 000 USD (converted from NZD)
I dont think i am on about the same bike as you or someone has a year wrong. I just got a 2006 Yamaha XT660R which is the off road type version which is a good bike and could do the trips you say you want, with some off roading in there for the crack. But they didnt make them untill 2004.
Anyway if the XT660R is what you mean and someone got the dates wrong i will explain the good and bad points.
It will handle off roading, not motor x style but off roading, you will probably need to get a bash plate, hand guards, screen and some form of luggage to tour on the bike. The seat is better than most off roaders but not as good as say a transalp. But the advantage over the transalp is it doesnt weigh as much so therefore you can go further into the bush. So to speak.
Now for some bad points. First off it is a single cylinder bike so there is vibe at around 70mph+ but you could with stand them for a while but for 2-3weeks at that all day not really, a twin cylinder would be better. But when are you going to be sitting at 70mph all day when you want to be touring. Second the tank is small, and at the moment there is only 1 alternative which is an offtheroad tank at 900euros or something stupid. But acerbis are being a large tank out this christmas at around £250 or so. That there or you bring a load of jerry/plastic cans.
I may sound blunt about bits but just trying to paint a picture about the bike. If you just wanna be doing on road with alot of it at 70mph+ i would maybe say the transalp or Vstrom would be better.
If the XT660R sounds good, go on here its got loads on info about the bike and there are alot of aussie member that could advice you about where maybe to get a good deal over there and bring it back to NZ land