I don't think the Greens donkey-votes will be enough to worry about as the election draws near.
The Greens have become a power-brokering party in their own right, and like Labor, have well and truly lost their way where their own parties ethics are concerned, and whilst I have always been opposed to some of their rather out-there policies, I do think I preferred them better when they were functioning as a genuine party, this opposed to the silent-supporters of someone else's.
Even Greens Leader Bob Brown is opposed to the system his party employ to earn themselves seats in the senate....well, so he says.
Guaranteed, if Greens votes are what determine the outcome of this election, this and manage to scrape Labor through by the skin of it's teeth Greens as a party will never live it down.
I think they know this which is why SA greens boycotted their national preference system (their How to vote Greens cards) , and I think others are contemplating doing this also...so you might find as the election draws closer and (IF) Liberal continues to increase in popularity, Greens balance-of-power may shift...as might their preferences.

I hope so.
They should listen to their leader on this, because it only stands to hurt their credibility more in the long run...should they be referred to the Australian Preference Party, APP, this and continue to lose touch with their own sense of political autonomy.
Seats in the senate or not, we are talking about the overall credibility of a party here, and if a 'clunker' Labor party wins this election, purely because Greens sold them preferences, then those who unwittingly voted 'How-to-vote-Green' this time, wont again next time, guaranteed, thus will cost them at the 2013 election after a dysfunctional Labor party has reeked it's havoc.
I would be trying to remain as neutral as possible if I were them, or at least preference both leading party's 60/40 (in favour of Labor) if they genuinely do prefer Labors climate or environmental policies.
Because at least this way, they wont be held accountable if Labor do manage to get in and destroys what's left of our economy...this and wont be left holding the baby.i