You say that you aren't really an expert in "United States," but in order to earn your united-states gold badge you needed to answer over 200 financial questions and obtain over 1000 upvotes on those answers. Only 17 users have managed to do that, and the thinking is that if you have been able to do that, you probably have an above-average understanding of financial matters in the United States. In addition, you must have been around long enough to care about the site and have an understanding of how it all works. You should know enough to know when you don't know enough to make a determination. :)
Of course, with great power comes great responsibility. It is good that you recognize that you now wield the dup-hammer, and you should only use it when you are confident. (I would argue that you should always be careful with votes-to-close, even if you are not the deciding vote.)
For me personally, I rarely vote to close as duplicate; not necessarily because I'm worried about being the lone, deciding close vote, but that I'm generally feeling charitable about keeping questions open and letting users answer new questions with new answers. I only close as duplicate when it is truly an almost exact duplicate; similar questions are not good enough to close for me. For a great article on the concept of duplicate questions, see Jeff Atwood's blog post "Dr. Strangedupe: Or, How I learned to stop worrying and love duplication." In it, he defends his realization that it is okay, and even preferable, to leave multiple similar questions open, and that trying to micromanage the site to contain one, canonical question for each topic is not possible.
In conclusion, I don't feel that the gold badge dup-hammer ability necessarily needs to go away, but I agree that those of us with the ability need to take the responsibility seriously and limit when we use it.
