Praise be on to Blizzard for these nerfs, but seems like they're still in denial about [card]Genn Greymane[/card] and Baku the mooneather breaking the game.
They will have to take those two cards into consideration whenever they nerf or release any new card, forever.
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You don't gain any net dust, though.
Regular Baku gives you a 1600 dust refund plus 400 if you dust him = 2000 dust. The math for an extra golden copy is: 3200 (refund) - 3200 (crafting cost) + 1600 (dust golden one) + 400 (dust regular one) = 2000 dust
Crafting the extra golden copy now only gives you a discount on the upgrade if you want to keep the golden one.