On the face of it, John Key's claim that s9 of the State-Owned Enterprises Act is "largely symbolic" and that the government "could not find a single instance in which it had been used" has to go down as one of the most ignorant political statements in recent memory. Section 9, and the subsequent court challenge to the then-government's plans to privatise away land and assets seized in violation of the Treaty, didn't just force the government to amend the law to ensure that claims could be remedied; it is where modern Treaty of Waitangi jurisprudence began. New Zealand Māori Council v. Attorney-General gave us a formal judicial interpretation of the principles of the Treaty, including the concept of the Treaty as a partnership (with obligations to consult and act on good faith), a duty to remedy past breaches and to actively protect against future ones. And those principles, refined and formalised, have guided the courts and government ever since.
For the Prime Minister to be able to make such a statement tells us two things. Firstly, he is profoundly personally ignorant of our constitution and the role of the Treaty. Secondly, he does not pay attention to his advice (because it is unthinkable that that advice would not have included such information). OK, there's a third option: that he's obeying his spindoctors and trying to downplay the issue and paint the Māori Party as freaking over nothing - but if so, he's not fooling anyone, and just comes across as stupid; see points one or two.
As for the issue, it matters. While land is protected, the SOEs the government is planning to privatise control other assets subject to Treaty claims - namely water and minerals - which are not protected. The sale of those SOEs may prevent those claims from being remedied. The principle of redress and the duty of active protection mean that the government needs to protect the rights of claimants to their remedy. This need not involve a general-purpose Treaty clause in the sale legislation, but it is going to mean caveating assets in the same way that SOE land has been. The problem for the government is that this will lower the sale price, making their already marginal privatisation project into a complete disaster. And while they can just bull on regardless, using John Banks' vote, that would come at the cost of a permanent break with the Māori Party, making them highly vulnerable to ACT boat-rocking or backbench dissatisfaction. But I guess in that case, Key will just blame MMP, rather than accept responsibility for his own inability to manage a coalition.