Martin Scorsese Is America's most consistently vital director, so Cape Fear, his first crack at a thriller, raises expectations. But this boldly imagined film is also Scorsese's first remake, which raises the question "Why Cape Fear?" Director J. Lee Thompson's 1962 film worked just fine, as did Robert Mitchum as Max Cady, the ex-con who takes revenge on a lawyer (Gregory Peck) by scaring his wife (Polly Bergen) and daughter (Lori Martin). Shot in black and white on a modest budget, the original…