I'm not sure why South Station isn't a great public space:
It's is a stub-end station with a vocation for commuter rail. Its doors open directly on the tracks, and that makes it chilly in the winter; South Station is not a place to linger, not even for a few minutes to finish the paper.
But I think South Station's real problem is the roof: It's not arched, like Grand Central or Union Station in DC, or the great sheds of Europe, like Waterloo, or.... or, what's that former train station in Paris that they made into a museum? The one where they crammed all the impressionists into an attic, and put the official art on the floor? Musée d'Orsay. South Station is not spacious. And it doesn't help that they sold what airiness there is to Tropicana.
Though I sure wish I had some orange juice now; the passenger who just sat down on the other side of the aisle is blowing his noise every two minutes and has a bad cough. This is why billionaires have private jets, I suppose. I think I'll go to the cafe car!
NOTE Also too, the trek from the South Station bus terminal to the South Station train station involves, let me see: One escalator down, a hallway [young man uncrumples tissue and ripely blows nose], the world's most slow-moving elevator, a hallway, a heavy yet narrow steel door -- passengers dragging luggage [young man blows nose] tend to collide here -- which gives on a zig-zag handicapped ramp, outside, followed by a station platform, the doors to South Station. Then one threads through the South Station crowds and kiosks to the Amtrak tickets station. Of course there's no signage anywhere; this is Boston. Who designed this?