There really isn't a single solution. We develop, acquire and manage such a wide variety of projects from paying a contractor for a single application to managing huge weapon systems over multiple years for multiple customers and integrated government and contractor team and we have essentially one acquisition system to do so.
To successfully pull it off (and it can be done despite what you read in the headlines) it requires a team of people that understand how to select the proper governance model and the authorities to stick to it and make sure the process is followed. However IME, the government at my customer anyway does not often empower managers to make hard decisions and control their processes. They then become frustrated and leave and the new manager then is left to pick up a program maybe half way through a development project. It's rare that they follow through and deliver a complete solution that really meets the requirements originally bought into.
The current mantra of agile development is not really making it better although not really developing requirements make it easier to declare success.
So, I'm not so sure the system is broken as much as we don't make sure that leadership teams of acquisition, engineering and management are built and that they are empowered and rewarded for successful programs. In my experience you get one or maybe two of those critical skills and try and muddle through and it inevitably goes poorly.
