Sorry to pop this bubble gentlemen, but whether it's 7 or 70 billion, it doesn't matter that much for two important reasons.
Firstly, the Governing Body can't sell them all because if they did, the Brotherhood would just evaporate, with no where to go.
And secondly, even if they were mortgaged, they would still have to manage the monthly repayments until their new investments turned a profit, which is easier said than done.
I grant you that it does sound very attractive, but leveraging a slow growth physical asset against the stock market ... is a recipe for an instantaneous implosion, with zero chance of recovery.
Doubt what I say ... then go mortgage your own home and try share trading. But the chances are, you'll be living in a tent within a year.
Besides that, has anyone considered what the Catholic Church is worth? Far more the 70 billion, I can tell you.