Though it boasts its share of high-tech gadgetry, the landscape depicted in “National Treasure: Book of Secrets” is in many ways sweetly old-fashioned. The plot hinges on one man’s quest to preserve the good name of his great-great-grandfather. The titular treasure is cherished not for its monetary value, but because, as one character exclaims, “This is going to give us incredible insight into pre-Columbian history!” Just as many clues come from dusty history books as from Google. And the president takes an enormous political risk based solely on his insatiable intellectual curiosity. Yes, this is a fantasy world, but it’s an appealing one.