The best thing about budgets in New Zealand is that they are just a little bit boring. Our fiscal conventions ensure big changes are telegraphed well in advance.

This year's Budget provides more capital spending for schools and hospitals, and a families' income package that has been long advertised.

More surprising was the substantial increase in tax revenues from stronger than expected economic growth forecast for the next several years.

Part of the reason for the expected stronger economic growth is that Treasury now forecasts that net migration will not drop by quite as much as it had previously expected. Stronger net migration means stronger economic growth, which means higher expected surpluses. And all of it gives the Government about a billion dollars more to play with per year than was forecast in December - $5.3 billion more through 2021/2022.

So long as the forecast growth is achieved, the Government can spend a lot more in total while not increasing tax rates.

The Government will need that headroom.

The envelope remains tight in part because of all of the things that are not in the budget, some of which are included in the tally of unquantified fiscal risks.

Pay equity claims for social workers, education support staff, school support staff and others are still in play and could be well above any budgeted contingencies.

The government is establishing a Canterbury Earthquakes Insurance Tribunal to resolve unsettled claims. But if that tribunal results in greater payments to Canterbury EQC claimants than EQC had expected in its last update, it's hard to see any allowance for it. Liability for dodgy EQC scopes of works remains completely unknown.

And provisions for mycoplasma bovis could easily run higher than the $74 million scheduled.

Another potential spanner in the revenue works – albeit an excellent one – could come through reductions in the tax collected from smokers. Tobacco excise sits at over $1.7 billion per year. That's about 2 per cent of all of the money collected by government, or about as much as would be raised by an increase in GST from 15 per cent to 16 per cent.

Tobacco excise rates are scheduled to continue increasing, and the total volume of tobacco sold is projected to drop by two percent per year based on prior trends. This month saw the legalisation of vaping and other reduced-harm products like heat-not-burn tobacco sticks and snus. There is no particularly good public health reason for taxing any of those.

If tobacco use drops by ten percent per year rather than two percent per year because people can now more easily switch to alternatives that less likely to kill them, the government will lose over $530 million in annual excise revenue by 2022.

So it is a good thing that the Government is maintaining wiggle room with relatively large expected surpluses.

Also strongly to the good were two announcements that came with the Budget.

James Shaw announced that the government will start working on an independent fiscal council in August. This body will cost election promises - so we do not spend another election debating holes - and will watch compliance with fiscal responsibility rules.

And, in questions during the budget lock-up, Grant Robertson suggested the government is looking toward more innovative ways of financing new infrastructure for urban growth.

The Government will be funding new infrastructure and will be using the Crown Infrastructure Partners arrangement for some of it. But rather than just taking it all on centrally, or forcing councils to take on more debt, it will be looking at new vehicles like infrastructure bonds, special purpose vehicles, public-private provider arrangements and targeted rates.

In growing American cities, the infrastructure for new development is funded by bonds, and those bonds are backed by a special levy paid each year by the people who buy the new houses. Council debt limits then do not get in the way of needed growth.

Letting infrastructure be self-funding through levies paid by the beneficiaries of that infrastructure is key to allowing new construction and unlocking housing affordability.

So the most interesting things about this year's budget are the things that are not really in it.

There are risks buried, or not even hinted at, in the revenue and spending forecasts.

There is opportunity hidden too. A larger infrastructure initiative would have been sorely tempting but is not sustainable over the longer term. Building better funding models can enable growth for decades to come.

And a fiscal council watching over election promises will also provide long-term dividends.

The Budget may have been a little boring. Watch for the interesting parts yet to come.