Finally, it's ours. After fifteen years of private sector asset-stripping and mismanagement, the trains and ferries are back in government hands, turning back the clock on one of the worst privatisations of the 90's. Unfortunately, the people responsible for that corrupt privatisation are still walking free, as are the scum who profited from it - but at least we've got the trains back.
As for what the government will do with them that the private sector could not, the short answer is "invest in them". The private sector's focus on short-term profit led to asset stripping and running a minimal service. But with oil prices rising by the day and a need to reduce transport-related greenhouse gas emissions, that's not a good long-term strategy for New Zealand. No matter what happens, freight and people are still going to be moved, but the market is unable to see far enough ahead to provide for it (face it: the market very rarely sees beyond next quarter). That provides a clear role for government in the ownership and management of rail infrastructure, just as it does for roads.
Of course, this sort of shift will also require policy changes as well, for example to make road transport pay its real costs, rather than continuing to be effectively subsidised by the government. And those changes are unlikely to happen under a future National government. Instead, they're likely to "leave transport to the market", entrenching existing inequities and repeating exactly the same mistake which led to rail being run down in the first place. The fact that this will then allow them to declare the renationalisation of rail a "failure" and flick it off to another of their cronies at a bargain-basement price again will just be icing on the cake.