Technically a part of Auckland's CBD, the Viaduct is the most upmarket part of the city center, providing plenty of eating and nightlife on a waterfront teeming with yachts and charter boats. There are about thirty establishments along the quay that include craft beer specialists (Andrew Andrew, Degree Gastrobar, and Brew on Quay), sophisticated cuisine (Euro and Portofino), crazy-good seafood (Soul, Waterfront Restaurant), and relaxing cafes (Number 1 Queen Street Cafe and Espresso Workshop). A wonderfully bustling part of the city, whether there is a regatta occurring or its just a busy weekend of people enjoying the quay, the Viaduct is an excellent choice to hang out any time of the day. You're also a short walk from the Westhaven Marina, where you can jet over to Devonport, or the Wynyard Quarter, an area in the midst of reclamation and redevelopment along the waterfront.
Note:Just to reassure you, there are plenty of nightlife options in the Viaduct, many of them of within the bar/pub range (sports bars, Irish pubs like O'Hagans), although quality dance vibes can be had with live music at Danny Doolan's and jazz just east at 1885 Britomart.