I dont think you can ever spend too much when it comes to peoples safety..thats just me though.
When that spending comes at the cost of efficiency in other areas it is too much. A family does not spend money on a fancy alarm system when they can't afford to feed their children. The US should not be spending as much as the rest of the world on defense when our education system is so deeply flawed.
We are about half of world spending- the entire rest of the world spends about the same amount as we do on military funding.