Either way, Helicopter Ben would be risking price inflation, and you can't eat bitcoins.
A country's economy is a complex beast. Trying to 'stimulate' it by controlling just one variable is a questionable endeavour at the best of times. One could naively hope that the money eventually trickles down to innovators who want to borrow cash in order to finance their big project. But what if:
-the banks aren't lending money to the public? Instead, they're just giving themselves fat bonuses and spending it overseas?
-regulations are stifling innovation?
-there is low public morale, making the business environment more difficult for innovators?
People in the US already own a large proportion of the available bitcoins. Imagine that the FED keeps adding more and more trillions to the balance sheets, thus causing a crisis, and people try to save their wealth from the hyperinflation by buying bitcoins. Sure, Bitcoin would then be worth a huge amount, but it would still only equal whatever value is required for the US economy to subsist. You might get lucky if you manage to convince other countries of Bitcoin's value, and you'll be able to gain a lot by exporting your new currency overseas (and thus continuing to import lots of oil, Chinese manufactured goods, and so on). However, a) Bitcoin is open-source, b) I doubt people will fall for the same trick twice.
You can not eat gold either
Same as gold and stock, theoretically they worth a lot, but if everyone is going to sell them for real goods, their value will drop like a falling stone, holding them and feel getting richer and safer is an illusion, but people like this illusion and they will spend more when they have this illusion
A human body is also a complex beast, but you just need some common sense to know his reaction without need to know how his brain works