@Mike I agree that more bike lines and 24 hour BART are more practical - and I support those ideas as well. I support practical ideas so much that my work involves trying to solve data-flow issues within cities.
But I would not dismiss this idea purely because it's "aesthetic": We carve elaborate designs on tall buildings that few people will ever see, we paint our houses pretty colors, we plant trees along our roads. In the long term, these aesthetic touches, and projects like street cars, have a real (and very practical!) impact on how a city develops.
Whether it's San Francisco, New York, Portland or Boston, we often see businesses pop-up near fixed transit lines. You do not see the same effect with bus lines.
Overview of the effect of fixed transit to population:
Relationships Between Business and Public Transportation
Impact of Streetcars in multiple cities