The Biennale of Sydney will this weekend throw opens its doors and lower the gangplank for its 21st birthday but instead of what should amount to a consolidatory, coming-of-age moment, the event has the pallor of a festival struggling for relevance.

For 45 years, artists from all over the world have clamoured for an invitation to the Emerald City's most-established contemporary art show.

Inclusion in the Biennale of Sydney was a feather in their cap, a platform to be seen by hundreds of thousands of visitors and the promise of other invitations to come.

The number of participating artists has fallen from 83 to 69, and where German curator Stephanie Rosenthal in 2016 commandeered more than a dozen different sites, this year's Japanese curator Mami Kataoka has reduced the biennale footprint to seven traditional venues.

Biennale of Sydney director Mami Katoaka. ( Supplied: Biennale of Sydney )

Behind the scenes, at biennale HQ, there has been simmering unrest about mismanagement and over-spending, culminating in the departure in recent months of four members of the leadership team, including the chief executive.

The ABC is not alleging these individuals were responsible for the alleged financial woes.

It was a coup for Biennale of Sydney to secure China's best-known contemporary artist and dissident Ai Weiwei and his monumental artwork Law of the Journey, a 60-metre-long inflatable, black-rubber lifeboat, packed with outsized faceless figures.

But such is Weiwei's fame that a separate preview day was arranged to reveal the boat at the former shipbuilding site, Cockatoo Island, lest the exhibition's 68 other artists be totally overlooked.

For a festival launched 45 years ago with a proud tradition of celebrating the shock of the new, Weiwei's boat is not new — it was on display in Prague, Czech Republic, for most of 2017.

Where film distributor Roadshow might not be listed among the biennale sponsors, it has sought to capitalise on Weiwei's visit, having timed the release of his refugee documentary The Human Flow for this week.

Which is all fine; showbiz feeds off cross-promotion and the international refugee crisis is a credible theme explored at length in the 2016 biennale.

Yukinori Yanagi's Icarus Cell, 2016, is on display at this year's Biennale of Sydney. ( Supplied: Tatsuhiko Nakagawa )

It was also at the root of the Biennale of Sydney's most recent significant upheaval, the 2014 artists' boycott over then-chief sponsor Transfield's offshore detention services provision.

This fracas led to founding sponsors, Transfield's Belgiorno-Nettis family, severing ties with the event and the financial impact of their exit is still being felt.

The downside of including Weiwei is a reduced number of participants overall and a pared-back vibe, where space is jockeying for art rather than the other way around.

In biennales, participating artists' travel, accommodation and installation is paid for.

They tend to fund their artmaking via government agencies, such as the Australia Council, or philanthropy, and if their work has commercial potential, they might sell it.

When Biennale of Sydney was launched in 1973 it was just the third event of its kind in the world and fashioned on the original Venice Biennale, which is still the world's pre-eminent contemporary art jamboree.

The Garbage Patch State, by Italian artist Maria Cristina Finucci during La Biennale of Venice in 2013. ( Reuters: Stefano Rellandini )

Now it jockeys for prestige among biennales too numerous to count, they can be found in cities as disparate as Marrakech and Kobe, Jerusalem and Montreal. It is possible to travel the world constantly visiting one after another.

In 2017, Sydney began to compete with itself, with a new event held in alternate years to the biennale, The National.

It is co-curated by three biennale venues: the Art Gallery of NSW, the Museum of Contemporary Art, and Carriageworks, and its focus is exclusively on Australian artists and they are funded to create their works.

Total visitors across the many Sydney Biennale venues in 2016 was officially estimated at 640,000. The National in 2017 was seen be an estimated 287,000.

Carriageworks, MCA and AGNSW will not release individual figures for each event, effectively preventing a clear evaluation of their relative success.

For that we need to look to the future.