Indeed. Any time there is a holiday or a sale is the right time to give Cash4Gold.
The gem/gold conversion rate works like a scale, much like the material traders worked in GW1, plus a two-way tax. It's an exchange that holds a giant pile of gold on one side and gems on the other. The price is dictated by how large one side of the scale gets. This pile does some great things.
Namely, it curbs spikes. Sure, people are adding gold and taking gems right now and the price is up, but just imagine it worked like the tradepost. You could imagine how the rate might be 10g/100 gems at the moment overnight. The two-way tax helps spikes, too, because it discourages speculation.
That's why I speculate/trade mini pets instead, as they are tied to the price of gold, but without the tax. Even better if you know the forging odds so you can "gamble" with the odds in your favor. Lastly, they tend to lag the gold spikes, so you can predict them getting a bump.