I think this issue is less an one of how much the United States spends versus what is spends this money on.
The question is in what kind of missions will the U.S. be required to be engaged. Without getting into the debate regarding whether we should have gone to Iraq or not, a careful anaylsis of the types of weapons systems the U.S. will need to fight future wars is needed to determine what weapon systems will be needed.
There are a couple of cultural caveats to this, however. The first is that the U.S. people are reticent to have even a single U.S. casualty. This means that protective systems must be as state of the art as possible, and that costs money. This would include shipboard systems, aircraft, as well as those for the individual soldier, airman, sailor, or marine. Please understand that I am not saying that these systems shouldn't be in place, but if this is the culture that we are going to keep, then it must be understand that it will cost.
Most of the military innovations today are in order to replace the man on the battlefield. That means more and more expensive technologies. But it also leads to the second cultural caveat.
Americans are increasingly unwilling to have collateral damage. But alot of this type of damage is caused by not having people in harms way. It is very difficult for the Hellfire missle on an aircraft to be discriminatory regarding who it kills when it explodes. And when that missle is fired by someone watching the target through a camera 1,000 miles away which is situated on a Predator drone, target discrimination becomes even more difficult.
And still besides, we must be able to defend ourselves from techologically advanced countries, such as China.
So the question becomes, what is the balance.
I can actually appreciate something I saw on the news regarding Obama's concept for the military. 40% will be dedicated to fighting a truly conventional war, 20% will be dedicated to fight in special warfare environments, and 40% will be flexible enough to fight in both. I don't know if he, or the military, will have the available mental capacity to be able to purchase systems that will be able to accomplish this goal, but the philosophy is at least somewhat sound.
But, I still predict that any military design will be heavily technologically based, which will cause the costs to rise.
In regards to the military helping in natural disasters, I believe the cost is still staggering. Usually this help comes in the form of Naval vessels, in some form or other. The cheapest operating cost that I could find for a modern naval vessel is $44,000 per day. And this is during its usual routine activities. These costs will necessarily increase during any type of emergency response.