Although it means staying at two hotels I'd overnight at the Auckland Airport Novotel, two minutes walk from the terminal, and head into town late the next morning after hopefully a decent night's sleep. I probably wouldn't be unpacking the first night anyway, just collapsing into bed. The second night I'd stay at the Hilton and walk to my ship when it was time to embark. That would give me an afternoon and a morning to see Auckland's sights (well at least a few of them). You can also go in by Skybus rather than a taxi. It stops a short manageable walk from the Hilton.