Almost any week of the year, you can experience the familiar sensation of a great performance in a lousy play. Debra Monk’s marvelous turn in Paul Weitz’s Show People, at Second Stage, is a more or less typical example. Miss Monk and Lawrence Pressman are cast as has-been old troupers who turn up at a Hamptons beach house in order to play the parents of a young tycoon eager to impress the girl he wants to marry. It’s not as simple as that, of course, but all the complications can be seen coming from a mile off. This is the kind of labored comedy-thriller that would have eked out a few weeks in the West End and Broadway of sixty years ago, when the defiantly sterile Hamptons beach house—all cold steel and glass panoramas—would have been a Gothic mansion, all wood paneling and French windows. Now it’s upgraded to the status of non-profit pseudo-art. And, given that, these days, “commercial theatre ...