Al Lenza’s parents traveled overseas three times after immigrating to the U.S. in 1961. Lenza estimates he’s taken 500 trips in 50 years. His home office is filled with self-printed books with recollections from each one. He’s working on more. The semiretired 70-year-old has already been to Barcelona three times in the past year. “You have more time and more money,” he said of his current phase of life. “The clock is running out.” American travel has transformed in recent decades. A nation of former homebodies has become one of zealous and moneyed international travelers, infiltrating every cobblestoned corner of…