I moved to Wellington last October. I'm still job-hunting, and have found the search a bit frustrating (a lot of weight is given to having NZ experience) but if you are a straight-ahead civil eng for roads, rail or construction then there are plenty of jobs about (have a look on seek.co.nz – you'll get an idea of salaries there too).
Wellington has worse weather than most of NZ but has good bars, restaurants and stuff to do, and still has ace singletrack on its doorstep (most of the riding I do here is steeper and more technical than anything I did before NZ, and there's a good trail centre at Makara Peak just out (rideable) of town).
I lived outside the UK before moving here; if you haven't there are other things to take into account, moving away from friends & family etc..