Many Americans got away from it all in the no-frills summer of '91-they just didn't get as far away as they used to. Vacation spots within driving distance of population centers prospered. Atlantic City gaming revenues in August were nearly 10 percent greater than in the same month last year. Lake Tahoe saw more Californians than usual, and Chicagoans went to Iowa for Mississippi riverboat gambling. Even New York's Catskills-which suffered hard times during the roaring '80s-had what one hotel spokesman called "our best year ever."