NADBank Enhancement Act of 2011 - Amends the North American Free Trade Agreement Implementation Act to authorize the President to agree to amendments to the Border Environment Cooperation Agreement between the United States and Mexico to change the purposes and functions of the North American Development Bank (NADBank), including changes that would allow it to finance infrastructure projects in the border region between the two countries that promote growth in trade and commerce between them, support sustainable economic development, reduce poverty, foster job creation, and promote social development in the region.