Well, nothing's stopping investments outside the empire (capital controls have gone out of fashion). This is one reason the rich get richer... Among the people who got the big tax windfalls, those who don't mind a bit of risk invest for high returns in developing nations... Helps the balance of payments in the investor's country. The others buy government bonds. None of this actually benefits their compatriots or the real economy in their country (except marginally through the provision of luxury goods and services).

Your point b is something I have always believed... Club of Rome and all that... It's about time it became fashionable.  

Indeed, it seems intuitively obvious that high rates of return on capital are only possible in a growing economy. So the risk-averse capital is not, in the aggregate, going to get a good rate of return. In the long term, perhaps investors will adjust their expectations to moderate, sustainable returns. In the meantime, with a huge amount of productive capacity idle, we've got a capital strike on our hands.

Government intervention seems the only rational possibility. But that would require rational government.

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}