Americans have expected to see their incomes grow from year to year. But that optimism has faded since the recession, and they now expect to make no more next year than they did this year. Their caution is one of the reasons the economic recovery has been slow and tentative. They’re driving their cars longer, and they’re not spending the way they did before. Moreover, while consumer spending had been recovering, it has slumped in recent months, stirring fears of another recession.