There are many reasons to relish a trip to Powell Hall when the St. Louis Symphony is in town. There's the beautiful old edifice, a converted movie palace restored to gorgeous splendor, from the gold leaf in the domed ceiling to the Art Deco proscenium and the plush crimson seats and carpet. There's the excited buzz in the lobby, where the monied old codgers whose donations keep the building open rub elbows (if unintentionally) with the college kids who scored $10 rush tickets — all of them dressed in their finest because a Saturday-night performance here is an event. There's the orchestra, a rich, well-tuned instrument, one of the finest in the U.S. And then there's musical director David Robertson. An accomplished musician who has received armfuls of awards and whose conducting skills are in demand all over the world, Robertson is also — and we say this in the most admiring way — a bit of a ham. Just watch him behind the podium! Robertson is a whirligig: His arms swing, his head bobs, his feet jig, his hair flies. He's an embodiment of not just the music but the joy of making and hearing the music. Which is, when you get right down to it, the reason we all go to Powell Hall.