I have what now would be a "trade" but when I bought it was just a book called "Mystery in Space" which reprinted all of the space heroes: Tommy Tomorrow, Star Rovers, Space Cabbie, Space Museum, Captain Comet and Adam Strange. I think it was published in the early 80s. So, the "pulp library" version you read sounds different - although perhaps it is a reprint of the earlier volume?
I vaguely recall the Twilight series as you describe it.
That said, it wasn't always the characters that made the stories - though I loved the Star Rovers and Space Cabbie - it was the kernel of scientific information that lay behind the stories - given Schwartz' background in SF publication - that I actually could use at school in science class to amaze and impress my teachers.