Labour's rejection of the Greens' pre-electoral offer

Labour's rejection of the Greens' pre-electoral offer to campaign in collaboration has caused some controversy among left-wing commentators, but let's look at what signals it sends.
The Greens' offer, even though it was rejected, has had a certain benefit for them. It has flushed Labour's true position out into the open. Now that left-wing voters can clearly see that Labour is contemplating putting post-electoral negotiations with NZ First ahead of any with the Greens, then it's likely that the Greens will probably steal a few undecided voters away from Labour. That's smart politics.
Labour's rejection says to us that their strategists have given up on the possibility of the Labour-plus-Green party votes being sufficient to get the numbers to govern. They predict that, if they have any chance of forming a government, they will have to talk with Winston Peters.
If Labour had accepted the Greens' offer, then Peters would have criticised both parties for doing back-room deals before the voters get their say, and he would have had to distance himself from them both. It would have annoyed him that one of his post-electoral options (a Labour–NZ First coalition) had suddenly become less likely, thus weakening his potential bargaining-power vis-a-vis National.
NZ First, as the centrist party, will most likely have options post-election, and Peters wants to keep those options open. Apparently, Labour wants to keep its options open too, so Labour won't throw its lot in with the Greens before the election. They are just being pragmatic about that.
If Labour have a shot at forming the next government, it would probably be NZ First to whom they have to offer the biggest baubles. After all, the Greens have no option but to support a Labour-led government. (Imagine the reaction if the Greens were responsible for letting National rule again!) So the Greens can be kept on hold. But Green voters need not be despondent about that, because the strong electoral results that the Green Party gets are probably thanks to their never having been in government! Supporting a government is usually electorally disastrous for minor parties.
All of this makes me ask why there is not (yet) a strong-ish minor party to the right of National, mirroring the Greens. After all, MMP does seem to encourage niche parties. ACT has fizzled out. But the Conservatives look like they are aiming to fill that space, especially once the John Key era comes to an end, as it inevitably must. The future contest will be whether the right-wing party is ideologically conservative or libertarian. ACT has shown that it's impossible to be both at once.
Getting back to Labour and the Greens, the MMP system, and the voters who participate in it, are probably better off having clear and distinct party brands that compete for their votes. Pre-electoral collaborations are not ideal. And in that I include those murky deals such as we see in Epsom.
The real doozy of a shady deal, though, has to be that which is contemplated presently between Mana and the Internet Party. That takes the cake. And, to mix metaphors, it can only end in tears. Maybe I'll write more about that later.