People want to watch "their" team win.
I have never, ever heard a fan (plastic, bandwagon or otherwise) of any sport say that they will/won't go to a game based on the nationality of those playing. And before you all get stuck in - you know what I mean.
We need the best players we can get within our circumstances - the more of those that are Kiwis then the better that is for the game in NZ... but to think that most "fans" (ie: the balance of the 30 thousand that turned up a few years back) make a conscious decision based on the number of Kiwis in the team (or not) then you are wrong.
Look at any sport you like... winning = better crowds.
At Arsenal they love Wilshire, at Liverpool Gerrard, at Man U it's Rooney and at ACFC it's Ivan Vicelich. It's only natural to identify more with your own countryman, particularly if they're special players. I agree about winning but you can't discount the local X-factor as well. Get both and you have the sweet spot!