You might be able to accuse the Greens of a few things, but avoiding scrutiny is not one of them

This election has given opposition parties an unprecedented opportunity to access bureaucratic advice and the Greens have taken it with both hands. In fact, the party has been so keen to access information from the Parliamentary Budget Office that the PBO head, Phil Bowen, must be almost wondering what he can do to get rid of them so he can get some sleep.

All up, the Greens have sent 74 policies to be costed by the PBO since 14 August.

You might be able to accuse the Greens of a few things, but avoiding scrutiny is not one of them. The easy argument in the past has been to just think of the Greens as economic vandals. Usually such statements are based on sections of their platform rather than any specific policies.

Certainly this election they have continued their usual policy of "tax and spend". In the past this might have been criticised, but when you have the supposedly conservative party funding a paid parental leave scheme that won't achieve any of its aims of increasing productivity or participation through levying a 1.5% tax on big business, it makes it tough to say the Greens are economic extremists. The Greens' PPL scheme is actually less targeted at the women who will be least influenced by it, and their policy costings revealed the hole in the Liberal party's scheme, which needed to be filled.

And this is the great thing about their list of 74 policy costings – they reveal the assumptions behind them and also the risks involved. Take, for example, their policy to amend the minerals resources rent tax (MRRT). The Greens say their proposals make the MRRT "more like that proposed by the Henry tax review".

The Henry tax review stated that a "uniform resource rent tax should be set at a rate of 40%". It was recommended to be for all minerals (except low-value ones) because "Australia has the world's largest economically demonstrated resource reserves of brown coal, lead, mineral sands, nickel, silver, uranium and zinc and the second largest reserves of bauxite, copper, gold and iron ore".

The current MMRT has a headline rate of 30% and applies only to iron ore and coal (and associated gas products). It also kicks in when profits exceed the long-term bond rate plus 7%. This compares with the original plan of the resources super profits tax which was set at 40% and which kicked in at the long-term bond rate plus 5%.

The Greens' proposal covers all minerals, is set at 40% and comes into effect at the long-term bond rate plus 2%.

So it is clearly a bigger tax than the current one. As such it is expected to raise more.

The PBO estimates it will raise $20.8bn from 2013-17. But the PBO has a few caveats attached to that figure. It notes that the costing "is considered to be of very low reliability". The reason is that "there is no direct tax information on which to base the estimates" and there is "no reliable information" on how those expected to pay the tax will react (that is, will they cease production and go elsewhere?).

Moreover, the costing model "treats each commodity as a single entity, so variations in company circumstances are not taken into account".

And finally, the estimates "are extremely sensitive to factors such as changes in commodity prices and the exchange rate".

Now that doesn't mean the $20.8bn wouldn't come to pass, but it does suggest you need to be careful spending all the money expected to be raised – or you risk coming up short like the ALP did with its expected MRRT revenue.

The Greens' plan would use the revenue from their MRRT to help fund their Denticare scheme, which would cover all Australians "up to $1,000 over two years for routine and therapeutically necessary dental care". It would be expected to cost around $8.5bn a year.

The Greens are also funding the scheme from a 5% levy on incomes over $1m (which is expected to raise $526m over the forward estimates), from ending fuel tax credits (which the PBO estimates are worth around $10.5bn over that period) and a levy on bank assets in excess of $100bn (which the PBO says would raise $7.9bn). So if their MRRT fell short, as did the ALP's version, there would be a budget blowout. But, while the MRRT is sensitive, by broadening the tax the Greens have made their version less sensitive to fluctuations than the ALP's. Moreover, the non-MRRT "savings" in 2016-17 alone are projected to raise around $6.2bn, so the MRRT is not doing all the heavy lifting.

The Greens also have full costings for a policy to co-fund with the states the construction of 5,000 new dwellings a year, and one to raise finance for the building of 7,200 non-profit homes. The Greens therefore have much more policy on the supply side of the housing market than does the Liberal party.

But above all they deserve praise because their policies are available and open to scrutiny.

Their MRRT policy costings for example, have been criticised by parts of the media. But it is an honest debate about the policies of a party that is mature and comfortable enough to put everything on display for voters and the media to see and evaluate.

Their approach should be the benchmark by which all parties in future elections are judged.