Here's a perspective:
NASA has accrued a colossal - and, indeed, expensive - super-critical mass of scientific and technological expertise.
Moreover - NASA has achieved big things. It embarked upon an astonishingly ambitious project, and succeeded. This is rare.
Dismantling this would be a waste.
However, the objectives of NASA (space travel/colonisation) are questionable. Do we really need to expand to other planets? The answer is unclear and the implications problematic.
Are there other things NASA could do that are clearer and more relevant? Yes. There is severe public anxiety about nuclear energy at the moment (Japan) - but we also have to cope with energy security issues and global warming (I hear you climate change sceptics - but can we save that for another thread, please, this guy has a project).
Nuclear fusion has the prospect of secure, clean, energy. It is, however, famously problematic. If, as NASA states, its expertise developed in the course of its projects is of benefit to humanity - and justifies its budget - it could apply some of this resource to the fusion project.
Resources might include: Personnel, training expertise, know-how, IT capacity, political pressure, project management.