a) His $1 million earns ~3% interest and depreciates by 2% per year, or
b) His $1 million earns ~4% interest and depreciates by 3% per year.
You're arguing that these guys are promoting multi-trillion dollar swings in the country's wealth in order to earn a couple more basis points on their investments. If you're going to posit a Greedy Ben Bernanke, why is he being so slow and cautious? He can probably make, at most, 1% per year extra by manipulating the value of the dollar. Or he could take a suitcase full of cash.