The wars in Iraq and Afghanistan have already cost taxpayers $314 billion, and the Congressional Budget Office projects additional expenses of perhaps $450 billion over the next 10 years. It is very obvious that it is a war too costly. However, the aims of the war are beyond economy, it is a political strategy-- it will affect Euro, a nail to Russia, Iran, and China. Also, in the long run, US can benefit from the war so long as US can control the oil there. For we all know that the oil is consumed much faster than before, and in a few decades later, the crisis of oil will be foreseen.
At present, the war doesn't only effects the US economy, and it cannot bring benefit to US economy in a few years, but also, it seriously damaged the world economy, too. Oil price has been sky rocketing, all the trades related have to increase the price too, in turn, we have to buy thing more expensively, beside the heavier tax to support the expenses of the war.
Usually, US economy benefit from wars. World War I and World War II had greatly increased the development of US economy. Also, US benefited from the first US vs. Iraq War. How about the second US vs. Iraq war? Can US economy benefit from it?
To conclude, the US will benefit from the war in the long run, not now.