The method I use to generate these maps cannot take a height map as input, so creating a height map (of a hill for example) first and then aligning streets to it is not an option here. Overlaying the streets with some kind of elevation markers (e.g. contour lines, as you suggested) IS an option, and I'll probably try this in the future, but not anytime soon.
If elevation is important for you, you can try using Village Generator with its hachures and shaded ground.