Dollar General is luring in more higher-income households as shoppers tighten their spending amid growing concerns around the economy.  CEO Todd Vasos told analysts during the company's first-quarter earnings call on Tuesday that new customers this year are shopping more often and spending more per visit compared with new customers last year. They are also allocating more of their spending to discretionary categories.   "We believe these behaviors suggest that we are continuing to attract higher-income cust ...