Not all Game Masters will refund gold or items. My friend's account was stolen some time back, and his Hunter and Paladin were stripped of their gear and gold. On the Hunter, he got only his gear back.
On the Paladin, the GM sent all of the gear Cash on Delivery, but didn't return any gold.
So there's a bit of a flaw in your trick here, in that there's no guarantee that a GM will refund gold and gear. You may get lucky and get it back, doubling your gold cache, or you may get screwed over, by the way previously mentioned.
Two years later that Paladin is still standing naked beside the Stormwind Mailbox at level 60, after numerous attempts to get a gear refund.
I don't in any way recommend this method of gaining gold, as it's quite a big gamble, especially if your characters are geared semi-well.