The Group of Twenty, or G20, leaders will gather in Brisbane next month with plenty of flashing lights and the occasional clown. Abbott's threat to "shirt-front" Russia's Vladimir Putin aside, there is a heady agenda on the table for the economists who want for global prosperity yet see pesky national regulations getting in the way.

But for all the hype and hoopla, doubly so for parochial Australia as host this time around, the G20 is a summit in trouble. "This meeting is a gathering of leaders looking for a task," was former foreign minister Bob Carr's candid reflection on the last summit, just over a year ago in St Petersburg. The stodgy communique had been decided by officials beforehand, leaving the assembled leaders to deliver a series of scripted remarks abounding with homilies and tedium.

Carr's memory might be tainted - after all, his recently published diary has him sitting at the summit table, famished and slightly delirious, imagining Barack Obama clutching Putin by the hips to form a conga line, dancing around the room to the strains of a tune about Brazil. But whatever his quirks of mind, Carr also gave a unique and very contemporary glimpse behind the closed doors of these big international summits.

The problem for G20 is its size. It is not restricted merely to the world's top 20 economies, but includes the European Union to represent its 28 member-states, despite Germany, Britain, France and Italy already sitting at the table. Spain is a "permanent invitee" as a consolation prize. Then a country to speak for African nations gets a place; one for south-east Asian nations, too. Australia has also invited Singapore and New Zealand along as guests to Brisbane.

And that's before we get to the unofficial hanger-ons, the L20 (labour) or B20 (business), C20 (civil society), T20 (think tanks and academics) or Y20 (youth).

The upside is the legitimacy this broad representation lends the grouping. The group covers roughly 80 per cent of the world economy. But the downside of having so many members is the risk that decisions will get bogged down in finding the lowest common denominator.

Australian officials believe Argentina makes a "meagre" addition, according to Carr, and for himself having listened to the rest, "there's little to inspire respect in the contributions I had just heard".

The G20 only became a leaders-level meeting in 2008 in response to the global financial crisis, promising co-ordinated economic stimulus to stave off an even worse recession. That action under stress was widely applauded as a success. What has never been clear in the years since is what role a summit of presidents and prime ministers - as opposed to finance ministers and key officials - can continue to play after the crisis. Leaders have incredible demands on their time and are often swamped by the issue of the day. In St Petersburg, Obama insisted the dinner talk was about Syria.

It takes leaders to make big decisions; it's a point often made to justify the G20. But in the corporate world and large organisations, the favoured number of management is for teams of about seven. Meetings then take less time, the group gets more personal attention, and the turn-around on decisions is shorter. Any bigger than seven and things tend to get tribal. The group divides and rivalries assert themselves.

Maybe the blame lies with human nature, but the G20 appears to be suffering this fate. There is obvious competition within the membership between the so-called BRICS nations of Brazil, Russia, India, China and South Africa, and the older Group of Seven nations, with the rest played off between.

Funny coincidence, that number, the G7. The elevation of the G20 was supposed to spell the end for that group, which had been a G8 before Russia got the boot this year after annexing Crimea.

But looking back at 2008, the opportunity missed for guiding the global economy was to reconstitute the membership of the smaller group to better represent the modern era, rather than expanding to the G20.

Why keep a moribund Italy at the table with the US, Germany and Japan and exclude China? Why not have a more nimble and powerful group with India instead of old-Europe's France? Why Canada, but not Indonesia? Or Britain, not Brazil?

Australia's officials or politicians won't make this argument for the simple reason Australia wants a seat at the table. But being part of a club with a bloated membership means missing out on the potential benefits of a stronger steer for the global economy.

The boast for the Brisbane summit seems to be the chance of attracting individual leaders to Australia for the first time in decades, such as an Indian prime minister. The meeting itself, despite importance of topics such as tax-dodging corporations or promises for better infrastructure, almost seems an excuse. The governance of the World Trade Organisation is an area leaders could usefully grapple with to break the logjam in global trade talks, but won't.

A wiser and lyrically minded colleague tells me, again coincidentally, that G7 is a very strong musical chord, one that often ends a song in that key. But musicians never invented a G20.

Daniel Flitton is senior correspondent.