Fractals are often used as a type of mind candy, in the sense that they are cool to look at and think about, but are usually not discussed in a rigorous way. In Fractal Cities: A Geometry of Form and Function, they are certainly used properly and are discussed in a highly quantitative manner. Unfortunately, since fractals are physical shapes, the book ends up mainly looking at the physical form of cities and does not delve into other factors related to cities (an aspect that the authors, Michael Batty and Paul Langley, acknowledge). While I must admit that I haven’t looked at the book in great detail, it certainly seems that it can provide lots of thought-provoking ideas and examples: mind candy of the healthiest kind.
Also, Michael Batty has written a more recent book called Cities and Complexity: Understanding Cities with Cellular Automata, Agent-Based Models, and Fractals, which also has a website that can be found here.