No, withdrawing from Iraq would not help the United States economy, because the economy would become unstable, with people worried about what would happen in Iraq. The war in Iraq is not a large part of the U.S. GDP, so the United States is not staying in a recession with constant commitments in Iraq.
The most recent figures I have seen suggest that the United States has spent more than $800 billion since 2003 on the Iraq War and subsequent presence. However, the most recent figure I have seen puts 2013 U.S.Spending on Iraq around $7.2 billion. That is roughly 0.02 percent of the 2013 federal budget and includes the salaries of the men and women still stationed there. That's not nothing. However, if the government brings those people home tomorrow, they still must be paid, or they enter an already-stressed job market. Iraq is, at present, a small part of spending and not likely to impact our economy significantly, especially since part of the current expense would not go away.