Hey David.
The wee Pajeros do just fine and are among the best bang for your buck for that kind of vehicle. Like all vehicles they have the odd issue but like most of a certain age the faults (and the fixes for them) are pretty well known.
Getting access to places to go off-roading is an issue for all of us. A lot of places will only allow access to properly organized clubs who they've come to agreements with. The Wellington Cross Country Vehicle Club is the largest club in Wellington and they have 2 "family shiny" graded trips coming up in September; One on Saturday the 12th into the Akatarawas and one on Sunday the 27th into the Orongorongos. Here's a link to their club page - give them a bell;
http://www.ccvc.org.nz/index.php/ccvcThere's also Odlins Road, aka Waiotauru Road, which runs off Akatarawa Road and is open to the public. Having said that though, it can be challenging at times (a few wagons have fallen off that track over the years) and it's a fair way of the beaten track so if you come to some sort of grief and you're on your own it can turn into a drama so you're best to tag along with someone else. There's some more info on Odlins Road on the ARAC (Akatarawa Recreational Access Committee) website ;
http://arac.org.nz/index.php/ Try searching "Odlins Road" on Youtube, there's some good vids people have posted.
Every so often someone on this forum might post to see if anyone in Welly-Town's keen on a drive so keep an eye on the forum. Just make sure your wagons got a proper tow hook at each end.
Have fun.