I had a similar 'Field of Dreams' view of Smugmug when I started as well. My advice is basically this: Smugmug Pro is a great place to support your photography business, but a Pro account won't create a photography business. It is simply a component of the business; one of the tools.
Simply offering nice photos on a website will not drive huge sales. In fact, you can consider yourself lucky if you sell enough to pay back the cost of the Smugmug account. The world is not waiting to buy your photos, but your customers very well could be. In other words, create a photography business first, and leverage Smugmug to enhance that business.