Investing in the productive economy hasn't yielded a positive return for the last ten years,

It depends on what you measure. Risk-free returns, maybe. Risky investments tend to do very well in expectation.

and yes, it's fair to expect the market to compensate you for deferring consumption because society is decidedly not indifferent between whether you consume resources now or later.

It would be nice to see an argument for this.

([U]nless you want all behavior to shift toward consuming all real resources immediately, including "seed corn", you have just as much an interest in seeing an economy strike a balance between present an future consumptio[n])

It seems that the economy is striking a sensible balance right now, with risk-free assets yielding about zero return and risky assets possibly yielding more. You'll not see any consumption/depreciation of capital, because if willingness to save falls then rates of returns will rise.

And getting people to invest in productive enterprises under threat of their money withering away is pure Machiavellianism

It's not. Currency "withers away" because it is effectively a risk-free asset which can be exchanged on demand for real resources (i.e. it has zero maturity) and its returns are standardized over large time-spans, including episodes of distress such as financial crises (whereas other assets are priced by the market and their returns might fall in such circumstances). This is pretty much the highest possible quality you could ask of any asset, and returns are adjusted accordingly. Bank accounts and money-market funds also have some of these qualities, but they have countervailing issues, and the interest they pay is meagre anyway.