Although viewed by some as juvenile literature because of the technology described in the works this collection does have merit as good quality SciFi.
The premise of the works is what happens when transforming technology is thrust upon mankind.This is what all good SF is about! The what could happen if? kind of question and the exploration of possible answers. So what would happen if a great deal of resources and effort were appplied to fringe areas of science research? Suppose the result was the discovery of an energy source based in the spacial relation of all matter and an economical means of using it! Suppose the result was also a group of medicines that could cure all and extend life indefinitely!
If these things occured what would be the economic and social impact? Might not the current global economy be disrupted beyond repair? Given the ability to leave earth and explore the galaxy would we not do so? Would our expansion into the reaches not entail the exploitation of resources, technology or of goods and services. Would we not possibly encounter other life?
Well, in the "Cities in Flight" collection the language used is definitely dated in the 1950's but the questions asked and answered are timeless. Thats what makes this good SF!