I don't think the Greens would need to sell their soul to go together with National. Actually, I don't think they can sell their soul given that they lost it a long time ago. Wouldn't it be fraud to sell something you don't have?
However - a coalition with National could help them to find their soul again - which should be to focus on the protection of the environment instead of being just another "me too" hard left whinge party ....
Who is running the Green party? The folks who used to run the "values" party and the "Alliance" - hard line leftists who took over the Green name as a cloak to cover up their real sinister and unwanted political ideas.