Aha, so since yesterday morning I've discovered that most of the Wellington transformative fen I know are going, as is a friend from Auckland. I would have already heard about this if I spent more time on twitter, which is where they mostly hang out. *facepalm* (Chances of my registering continue to increase, even if that does mean making a decision before tomorrow night.)

I'm fond of the zoo, but have no idea how it compares internationally.

Other off-the-top-of-my-head things to do in Wgtn (you may have already found some of these via googling):

Walks: https://wellington.govt.nz/recreation/enjoy-the-outdoors/walks-and-walkways
Ferry to Matiu/Somes Island: https://en.wikipedia.org/wiki/Matiu_/_Somes_Island
Bike rental: https://switchedonbikes.co.nz (these are my go-to people and where I bought my ebike; there are other bike rental places too, of course)
There are umpteenzillion independent cafes, each with individual weirdnesses. Most of them are good at accomodating dietary restrictions; I'll ask around for ones with good selections of tea. :-)
I can organise a local transformative fen meet-up, if you want to meet people before WorldCon and increase your chances of seeing familiar faces in the crowd. (We occasionally go out to dinner for fangirl Fridays, but have been known to manage other days of the week when required. ;-)