Americans have a chance to recoup some of the 45% net worth decline that they suffered during the financial crisis, but will they seize the opportunity? Most won’t. But the smartest ones will.

What opportunity? A chance to buy stocks when their earnings growth prospects exceed their price/earnings ratio.

There’s plenty of bad corporate news out there – Japan’s earthquake destruction is cutting supplies of semiconductors and boosting their prices, in the last two months, oil prices have risen 32%, or $27.21 a barrel to $112.79, since February 11, 2011’s $85.58 (likely to lead the International Monetary Fund to cut the U.S.’s 2011 GDP growth forecast from 3% to 2% or below using the IMF’s assumption that a $10 boost in the price of oil lowers economic growth by half a percentage point), and prospects for more partisan standoffs in Washington that will inevitably lead to budget cuts that reduce economic growth slightly.

But none of that bad news can change the fact that stocks have risen an average of 23% a year since Barack Obama became president and that the alternatives to investing in stocks are yielding around 0.02% — far short of March’s 1.2% rate of core inflation. Of course, you could always take a look at commodities ETFs as a way to play the rising prices of items like oil, corn, wheat, and cotton that are driving up what consumers pay for food and energy and yielding a 2.6% overall inflation rate.

But human emotions are more powerful in controlling what many people do than their intellects. So only those who can overcome the emotional resistance to buying stocks will benefit from their rise. And there is ample evidence that many are swapping their cash for stocks.  For example, cash in money market funds has fallen 28% from $3.8 trillion at the beginning of 2009 to $2.74 trillion in March 2011.

Meanwhile money flowed into stocks in 2010 with funds chasing global stocks exceeding the outflow from U.S. equities. According to TrimTabs, $87 billion in funds flowed into global equity funds in 2010, up 40% from 2009’s inflow — while well south of 2007’s $182 billion inflow peak. But money has been steadily flowing out of U.S. equity funds over the last three years — albeit at a slower rate. Specifically, in 2008, $42 billion flowed out; in 2009 outflows rose to $47 billion, but declined to $38 billion in 2010.

While money flow statistics suggest investors running from stocks, their earnings prospects remain at a robust 17% for 2011 growth — well above the 9.5% quarterly average earnings growth, according to Bloomberg. In light of the S&P 500’s modest forward P/E of 14.1, this suggests that stocks are valued at less than their anticipated earnings growth rate. Moreover, with some 71% of companies beating expectations in the most recent quarter, the prospects for further stock price increases on a wall of worry look compelling.

Even if stocks grow at half their recent 23% trajectory, they’ll soundly beat the 0.02% they’re earning in money market funds.