I don't think it devalues the gold badges much. Consider that many gold badges will become much easier to earn when the site will have more regular visitors, as good questions or answers will get more upvotes and more views. The Fanatic badge, however, won't be easier to earn, ever.
As for your worry about employees finding out that you're visiting Mathoverflow much, this might happen, but I don't think the Fanatic badge alone changes this much.
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