After all, Peters has not been shy when it comes to making expensive promises up and down the campaign trail, be it abolishing GST on food or reopening the uneconomic Napier-Gisborne rail line.
Moreover, unlike Labour and the Greens, New Zealand First has yet to produce a detailed fiscal plan or alternative Budget which lays out exactly how the party intends funding its spending promises.
Rather than highlight that, National may be offering something of a timely olive branch to Peters, knowing that he knows National knows that the poor showing in the polls by parties on the left is inevitably leading him to National's door.
There is another reason why National is not including New Zealand First in its "tax and spend" equation, however.
Although he might sound profligate before an election, Peters, who was Finance Minister for two years in the 1990s, has been pretty responsible when it comes to spending taxpayers' money. Painting him as a spendthrift does not square with his track record.
Having spent their whole time in Parliament in Opposition, the Greens do not have a similar track record to fall back on.
That makes it a lot easier for National to indulge in scare tactics. Adding New Zealand First to the mix only makes a simple message more complicated to get across to voters. In contrast, bringing Internet Mana - and its promise of free tertiary education - into the picture makes National's spending warnings even more potent.
Of course, David Cunliffe has ruled out Internet Mana being involved in any Labour-led governing arrangement. But then he has to do so before the election to protect his vote. As everybody knows, afterwards can be a very different story.