Well, he could spend it on ships and guns. He kinda has a manpower crunch, and the obvious answer is slaves, to the point it is assumed any major construction like the pyramids must have directly involved slaves. It is probably safe to say conflict with spain/Charles is inevitable, because he has a shortage of willing manpower, and the obvious answer is slaves, which we also just so happen to be a market our navy has sworn to strangle, which would massively hobble the growth of new Spain. Plus, with our money value being tied to gold, the sending of wealth could itself be a weapon against those denying growth.