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Riding on the back of a motorbike is probably the best way to see Vietnam’s capital.  The hair-raising experience lets you feel the energy on the street, the incessant buzz of small businesses, the informal sidewalk kitchens, and the surprisingly large numbers of Western tourists gawking at the fading yellow French colonial architecture. Compared to other economies in Asia, Vietnam seems a sure growth bet for the next quarter century. Yet capitalizing on that potential will task the government even as it eyes closer relations with its erstwhile enemy, the United States.

The plethora of goods, restaurants, and crowds make it easy to forget this is still a Communist-run country. Everywhere one looks, newlyweds in their wedding best pose for pictures, dotting major...