Especially for some of the less frequented tags, such as matlab, it can take a long time till a question is closed as duplicate. (For example, How to load a series of files into MATLAB matrix via loop has been up for closing for over a week.)
Given that gold and silver tag badges usually mean that a user has spent quite a bit of time answering questions, user with these badges are also more likely to remember the duplicates, which may have a non-intuitive title, and thus not show up in the automated search.
I suggest to give the more (e.g. 2-3x for gold, and 2x for silver) weight to gold and/or silver tag badges for close-as-duplicate votes (of a question with that tag, obviously), to make the duplicate questions disappear more quickly.
NOTE Three years later, a similar suggestion was very positively received (see link to duplicate)