When Gore Vidal’s “Visit to a Small Planet” opened on Broadway in the late 1950s, it was intended to be a satire of the world’s superpowers in their hunger for control during the Cold War. Although times have changed, the play has held up remarkably well, as can be seen in its lively production at The American Century Theater. The improbable story starts in 1958 in the home of Roger Spelding (Steve Lebens), a television broadcaster who lives with his wife, Reba (Kelly Cronenberg) and his nineteen-year-old daughter, Ellen (Megan Graves). Ellen’s boyfriend, Conrad (Noah Bird), is always at hand.