You get a full dust refund for having them, not a full dust refund for disenchanting them. If you have a normal Baku, and you spend 3200 dust to craft a golden Baku, you get 3200 dust back with the rotation. After that, you can do two things - disenchant your golden Baku for 1600 dust or disenchant your normal Baku for 400 dust. So, you either end up with your original normal Baku and 1600 dust or a Golden Baku by spending 1200 dust. But if you do nothing, your normal Baku will net you 1600 dust anyway, rendering the first scenario redundant. So the only reason for you to craft a golden Baku is if you want the second scenario. You can upgrade your normal Baku to a golden Baku by spending 1200 dust. In no scenario will you gain any dust by crafting a golden version of a card which you have the normal version of.