This strikes me as an intelligent idea that hasn't been tried here: Forcing bureaucrats to justify their spending. In a court of law, which side has the burden of proof is an important advantage. The way budgeting is currently structured, the taxpayer has the burden of proof to attack a particular bit of spending and show that it is unworthy. Why not reverse that? Those who are spending our money must be prepared - not to defend against a cut of their budget, but to make a positive case for that which they wish to spend. Reverse the burden of proof. I think the really valuable government actions will rise to the top pretty quickly.
Tedious? Sure, but compared to what? Open to abuse and manipulation? Sure, but any more than the current system? Time-consuming? I call that a feature, not a bug.