Mr Norton's reasoning suggests the party may be vulnerable again.
"I'm tossing up between Labour and the Greens. I like the idea of a capital gains tax but I don't like some of Labour's other policies," he says. "They [Labour] are talking about repealing the 90-day trial period [for new employees]. I want that to stay. That will probably put me off voting for them, to be honest."
But the Greens would also scrap the 90-day trial period, as would the Maori and Mana parties.
Others are equally uncertain. Mathew Pou, an 18-year-old IT student at Unitec, is also tossing up between the Greens and Labour but leans "more towards the Green Party".
Wellington osteopath Karen Rodgers, 46, says her choice "might be the Greens".
"We're just fed up with both Labour and National."
Takapuna radio producer Benjamin Paul, 21, says: "I usually go for Labour but I don't think they're up to it, they're not very ballsy.
"They're trying to be a little bit too opposite to National but they are not really. So I'm voting Green but it's a bit of a protest vote."
Even some of the Greens' core supporters who have backed them through each recent election, such as Christchurch builder and ski patroller Michael Ward, 46, echo Mr Norton's thinking.
"They are the conscience of the country," Mr Ward says. "I wouldn't want them running the country but I think it's important they put the handbrakes on the big parties, get them thinking about the environment."
On a rough count, about 44 of the 65 Green voters in our sample are passionate about core Green issues of environmental and social sustainability.
Brenny Dye, a 42-year-old Mt Maunganui mother of two, says: "The biggest contribution this country can give to the world is its green environment, and Key wants to just drill for oil."
Jackie Scott, 63, a Christchurch counsellor, votes Green because "I have grandchildren and want them to have a world".