On Mt Roskill electorate the concept that it is heartland labour is just wrong. The centre of the electorate, Mt Roskill & Mt Albert are low income areas and are heartland areas. But the fringes, Hillsborough, Mt Eden, Three Kings, Lynfield are all becoming/have become upper middle class as state houses are converted into do-ups.
At current rates I would expect Month Roskill to be a safe national seat in 20years, with the low decile population moving out West/South in a similar manner to what happened in Ponsonby.