Too much of a good thing can become a problem. Soaring home values in the Dallas area have lifted the net worth of thousands of families. But for many renters and others on the outside, a new home in Dallas is now beyond their financial reach. That’s discouraging for entry-level buyers, and it could create headwinds for an economy whose low cost of living has attracted newcomers for decades. In a measure of affordability, the Dallas area has lost major ground. In 2010, nearly 80 percent of new and existing homes sold in the area were affordable to families earning the median income. By late 2016, just 50 percent of the homes were considered affordable. Dallas is still a much better value than San Francisco, Los Angeles and New York. But they are not our only rivals for corporate relocations and college grads. Chicago, Atlanta, Phoenix and most other cities have a more affordable proposition today. The North Texas economy keeps rolling on, because there is more to the region’s success than home prices. Yet affordability remains a concern for buyers and builders.