There is also a lack of agreement on whether the SDGs should commit rich countries to curbing their consumption of natural resources, in order to leave more for the poor.
In a widely-circulated editorial, former Soviet President Mikhail Gorbachev, who now runs Green Cross International, contrasted the "optimism and hope" of the Rio Earth Summit 20 years ago with the "cynicism and despair" surrounding this one.
"I feel bitter when I look at the cavernous gulf between rich and poor, the irresponsibility that caused the global financial crisis, the weak and divided responses to climate change, and the failure to achieve the MDGs," he said.
"The opportunity to build a safer, fairer and more united world has been largely squandered."
The eight rounds of formal and informal preparatory talks since the beginning of the year have been bedevilled by problems of substance as well as of process.
Some Western nations, especially the US, appear unwilling to give ground on anything that would help rival up-and-coming economic powers, in particular China.
They, meanwhile, are reluctant to countenance any language that could put a brake on their development.
The summit also falls in a difficult political period, with the US presidential election due later this year, an impending change of Chinese leadership, and many nations struggling under various financial issues.
Following the close of the preparatory negotiations this coming Friday, there will be four days of informal dialogues and other meetings before heads of government and ministers begin the summit proper next Wednesday.
There is widespread disappointment among activists that scores of leaders including the UK's David Cameron, Germany's Angela Merkel and US President Barack Obama have chosen to stay away.
The US has however confirmed that its delegation will be led by Secretary of State Hillary Clinton.