For the next couple of months, if National Prime Minister John Key thinks there's any hope left for the ACT Party, he'll spend some time providing symbols that will infuriate the economic right. He'll look for ones that are relatively cheap, like appointing "history's greatest monster", former Finance Minister Michael Cullen, to head up New Zealand Post (history's truly greatest monster here). Cullen won't do any worse than the average appointee to that position, but he'll rile up the folks who'd be at the margin between ACT and National.
When and if he's lost hope that ACT can ever get itself together, those symbols disappear and he starts pushing a more liberal economic line, or at least providing those symbols. He can't go as far as Brash did, but he can certainly destroy ACT without much effort - kill Epsom, and tack slightly more right on economics. He won't move far in overall positioning - it's worse that moderate voters switch to Labour than that hard core economic liberals just stay home on election day. The former counts against you twice while the latter counts against you only once. National then moves farther to the right in the longer term as it absorbs former ACT activists into its party base.
The day Key stops attacking Douglas and starts talking up economic liberalism, dump your ACT stocks at iPredict.