Eighty prominent Australians, including a former head of the Australian War Memorial, have signed a letter opposing the planned $500m expansion of the memorial under its current director, Brendan Nelson.

In an open letter published on Saturday, the signatories say the plans glorify war and the money would be better spent helping veterans with post-traumatic stress disorder.

It has been signed by a former director of the memorial, Brendon Kelson, former deputy director Michael McKernan, and Paul Barratt, a former secretary of the defence department.

Novelists Tom Keneally and Richard Flanagan, historians Henry Reynolds and Stuart Mcintyre, former Western Australia premier Carmen Lawrence and former human rights commissioner Gillian Triggs are also involved.

The $500m expansion would nearly double the size of the visitor area, create a new hall to display the memorial’s aircraft collection, and establish new exhibits focusing on contemporary conflicts, and deployments in Afghanistan, Iraq, the Solomon Islands and Timor-Leste.

It would also create a place for private reflection for visitors.

Barrat told Guardian Australia the plans were a waste of money and ran the risk of turning the memorial into “a military theme park”.

“There are an enormous number of living veterans who are suffering greatly from PTSD from multiple deployments to Afghanistan and the like,” he said. “I think it is obscene to be spending these amounts of money on a memorial when we’re not properly looking after the living veterans.

“There seems to me to be a very great danger of converting it from a solemn memorial into a sort of military theme park … I think the war memorial as it is, is a perfectly adequate memorial to the conflicts of the past. Let’s look after the living before we further memorialise the dead.”

The letter also opposes the plan to demolish the existing Anzac Hall, which in 2005 won the Sir Zelman Cowen award for public architecture.

“The memorial should be revered but Australia has many stories and Dr Nelson’s excessive veneration of the Anzac story denies the richness of our history,” it said.

A spokesman for the memorial told the Canberra Times the majority of Australians supported the expansion.

“A decision had been made by the Australian government to support the project, as the overwhelming majority of Australians do, and it will proceed as planned,” he said.

“The memorial’s mission includes leading the development of understanding of Australia’s wartime experience. A worthy part of this is enabling veterans to feel the memorial is a safe space for them to engage with and own their stories, and those of their predecessors.”

Announcing the funding in November, the prime minister, Scott Morrison, said in a statement it would honour the achievements of recent servicemen and women.

Morrison said the government was investing $1.4bn into services for veterans like free mental health care and a “fairer indexation of defence force pensions”.

“Our $498m investment in the Australian War Memorial’s redevelopment will help them tell new stories in new ways,” he said. “The redevelopment will increase visitor areas by 83% or around 10,000 square metres to expand the exhibition and public program space which is currently at capacity.”