I think NZ have learned their lesson well.
They were very foolish to get involved with the disaster waiting to happen that was AN. The unprofessional NZ management of that era allowed themselves to get panicked into the foolish decision of going from a 50% stake in a dying airline to a 100% stake in a dying airline - if they had done a due diligence rather than panicking they would have known not to throw good money after bad. They should have allowed SQ to buy the other 50% AN would still have died (let's be honest, it was such a mess of over staffing and absurd fleet decisions that nothing could have saved it in a deregulated environment ) but NZ would have taken much less of a hit both financially and reputationally from the demise.
VA is showing every sign of turning themselves into AN mark II and NZ should exit as quickly as possible.
Without the artificially protected environment of the two airline policy the Australian market simply isn't big enough for two full service carriers. Virgin Blue may have been a bit rough around the edges, but I would argue they were far closer to what the market needed ( and could support) than Virgin Australia's attempt at being a second Qantas.