Public transport works really well for getting in or out of a CBD... going across a city, it, unfortunately isn't as good. My wife loves catching the train to work.... be then we only live just over a km from the Manukau station and her work is less than 300m from the Britomart/Waitemata station.
When she was at Newmarket, it was a totally different story as the trains don't go from Manukau to there, so she'd either have to leave a car at Homai or Papatoetoe or swap trains at Onehunga. It was easier for her just to drive in.
Be interesting to see how well the bus lane from Botany (when the last section is finished) through to Panmure goes. Funny thing is, I thought it was a government promise to pay for the whole thing entirely once the regional fuel tax was removed but NZTA are getting Auckland Council to foot half the bill for the last section from Guys Reserve to Botany.
BTW, even though your daily commute would be $18, AT have a system where, if you use the AT HOP card, the maximum you have to pay is $50 each week. That means you'd get two days "free" travel... if you wanted to put up with 3 1/2 hours travel each day.
-day fare cap for Auckland public transport
at.govt.nz