I argue that we have a reasonableness standard we can apply here - "Lack of consideration" is what might void a contract indenturing a 20 year old idiot in an unpaid MLM scheme.
Consideration of the public is a factor.
> "Chicago's 2008 parking meter deal, a 75-year, $1.16 billion lease to private investors, is widely criticized as a lopsided, "worst practice" agreement. The deal, pushed through in 72 hours under Mayor Daley, forces the city to pay "true-up" fees for lost revenue, resulting in over $2 billion in revenue for investors [so far] while the city continues to settle costly disputes."
People are ignored, councils seem to rubber stamp things and the tactic at higher levels is to make a terrible decision and then attempt to use courts to delay any attempt to stop whatever the decision was. When it’s finally stopped, it will be done again slightly different and restart the lengthy court process.
The big problem is long term outsourcing contracts, that serves to get the debt off the government’s books. If anyone else did it they would be required to show the debt under off-balance sheet financing rules, but the government gets to set its own rules and gets away with hiding the real situation. Gordon Brown did a lot of this so he could pretend to have balanced the budget.
Apart from central government a lot of local authorities have done this too. Sheffield's notorious street management contract (the one that lead to cutting down huge numbers of trees) is a good example.