I think in order to eliminate politicians' "sacred cows" and to neutralize the threat of constant earmarks, the tax payer should be allowed to determine - at least a percentage - where their tax money goes.
Some value healthcare over others and more value national defense, etc. Well let the taxpayer put their money where they feel best.
In the age of electronic voting you can pick your president but you can't determine where your money goes?
Start off small and see where it goes. Let the taxpayer pick exactly where they want say 10% of their $$$ to go. Create a system like filing your taxes or incorporate it into that system. Let them pick and choose.
You will find out very quickly where people's interests lie...
Ultimately it is up to WE THE PEOPLE.