Thanks again Blackcloud, you've been really helpful. And yes, it would be brilliant if I was lucky enough to be guested - but I know Dec/Jan are busy travel periods so I shall have to wait and see
Edit- I could earn 1 mile/mile travelled with BMI (fare classes M and Q) - if I add up the km quoted by AirNZ and convert to miles it gives me about 23000, if I use some random airline mileage calculator it gives me 50,000! Reckon the former to be more likely - and it would give me some free flights to use in Europe/N Africa - thanks Blackcloud for the advice.