The question of whether smartcarts are truly smart investments got a brief exploration in a recent AP story, that spoke of the struggle of smartcarts to make money, but that seemed to miss the point. Ultimately, yes, Smartcarts are intended to boost profits and sales and I believe they will, assuming the CRM-friendly data they generate is put to shrewd use.
In the short-term, though, they have a much more urgent goal: stop the customers from going elsewhere. They are there to show customers that grocery stores can indeed make shopping efficient and fun again. But like any other sophisticated piece of retail technology, they won't work if they're not integrated into the store. A store that throws them out there with just a bunch of videos in the screen--as depicted in the story--deserves to lose its investment.