The U.S. is already the most powerful country in the world militarily. We are already spending so much that in order to fill the budget the military is buying items like tanks that they do not want or need just so that they can scrap them later. Any reduction in weapons is a good thing in my opinion.
No, the US should never sign the UN weapons treaty since it takes away Americans' basic rights to gun ownership. It is apparent that the second amendment gives all Americans the right to bear arms for protection and to own guns, and signing the treaty would infringe on those rights.