"Generation X was hit the hardest," Emmons said. "For those families themselves, there's limited time to make up some of those losses. For the economy overall, families that are struggling pretty hard to make up their savings aren't spending as much, so that's a drag."
The median value of mortgages and home-equity loans held by 35- to 44-year-olds climbed to $131,000 in 2007 from $85,000 in 1995, based on Survey of Consumer Finances data.
Then property values tumbled during the real-estate crash. For 35- to 44-year-old homeowners, the median value of a primary residence dropped 21 percent to $170,000 in 2010 from $215,000 three years earlier.
As more decided to rent rather than own after the downturn, they've missed the subsequent rebound in home prices. About 60.7 percent of 35- to 44-year-olds owned a home in the first quarter 2014, down from 68.3 percent in the first quarter 2007, according to Census data.
Gen-Xers were also slammed by the slump in stocks. The 35- to 44-year-old age group's median value of financial assets, including stocks and bonds, dropped 47 percent to $14,500 in 2010 from 2007. The hit to their portfolios was more than 5 percentage points bigger than for any other age group.
The value of the group's directly held stock portfolios lost 36 percent, Fed data show. While those who stayed invested in stocks may have recouped losses as the S&P 500 Index has rallied to new highs, only 12 percent directly held equities in 2010, compared with a 17 percent share three years earlier.
What's more, limited improvement in the labor market is making it more difficult to rebuild assets.
"It looks pretty bad," said Amir Sufi, an economist at the University of Chicago's Booth School of Business. "If you don't have income, you can't build wealth."