Good on Gareth for raising the issue - who knows how much of his purpose in raising it is a negotiating ploy and how much is a serious proposition but a discussion well worth having either way.
The fundamental problems with Westpac are: it is an oval stadium hosting predominently "rectangular" sports and it has no roof in a city with a dodgy climate. Its huge strength is its absolutely brilliant location - walk to town, by the main railway station and just off SH 1.
Moving the Nix out of Westpac would kill its viabilty - rugby can barely afford to pay the playing day charges now let alone the increase in cost they would incur with no Nix games. Something would have to give.
Petone and Newtown are, by comparison, terrible locations.
It would take some political courage (and probably or a few guns held to heads by stadium clients) but I think a study should be commissioned on converting the stadium in to a rectangular stadium with a roof - the concourse is done and I suspect a fair bit of the foundations could be utilised.
In parallel the Basin could be tarted up, if needs be, to ensure it meets the needs of "oval" sports although it seems to already be rated as a great, traditional, cricket venue.
This makes more sense to me (at least knowing the feasibility and cost of conversion) than spending $30m on a stadium in some hard to get to location and turning Westpac (a community owned asset) in to a white elephant.