If the Government's surplus was speant in the current climate the economy would overheat. Inflation is already at its maximum range in the 2-3% goal region, and so any more Demand side stimulation, which would be caused by an increase in government spending, would have the effect of increasing demand push inflation, suppliers then would not be able to keep up with the excess in Demand, and buyers would, in effect, bid up the price of goods, causing cost pull inflation. You'll find that the idea of spending to come out of a recession, or a time depression on the cycle, into, at times, a defecit, and that during times of economic expansion having a surplus is not unusual. Like I mentioned before it's an idea Adam Smith came up with in 1890's.
The only way you can overcome this is buy offering more incentives on the supply side to increase production; as the economy is at full employment, this is difficult. It doesn't help that Gillard says that Big business' will be hurt if Labor is elected, it is important to have producer confidence high, and to give them incentive to expand operation, not to penalise them for doing this. That is the main reaon why I fear a Labor Gov would have negative effects on the economy, I don't think that they will be able to deal with the economy performing so well, it doesn't happen by accident.