Hey!
This is a nice quote for a discursive piece! Discursive pieces are great, because they are quite flexible. You can make this quote fit into your own interpretation and whatever you want to write about.
The main idea of this quote that jumps out at me is the imagined reality of literature - one can fall in love with cities and people they've never been to or met through reading. Falling in love with the scenery, atmosphere, and characters of a book is a common experience for many of us. Alternatively, this quote might fit nicely with a discursive piece about travelling, or ancient/futuristic civilisations? It depends entirely upon what you're interested in and how you interpret this quote!
Just make sure in writing it, you utilise discursive techniques, and decide whether your tone will be formal or informal!
Not sure if you are required to write a reflection, but what I found very effective, is analysing the techniques from a prescribed text (Mod C) and using these in your piece. This will give you a basis of what to study for in the HSC (you may be required to write a reflection - so you will need quotes) and also make sure you have included some typical discursive techniques.
As for coming up with ideas, that is something we all struggle with. My best advice would be practice. Look at a bunch of stimuli and practice brainstorming ideas. The more you do it the better you will become! (Cliche, I know, but it is true). Other advice would be to break down the stimulus - highlight the key words and write anything that jumps out at you, and hopefully a combination of related ideas will give you a foundation.
Generally, reading and research really helps in being creative. Having knowledge of the world and of literature allows you to form connections between your work in HSC English, and other ideas. This is especially true for take-home tasks because you have the luxury of being able to research the exact topic you like!
In an exam setting, I would revert mostly to the practice idea. It is commonplace though, to go into the exam with a broad idea. Many students memorise a brief idea, something that they can mould into any stimulus, so that they do not panic in the exam, in case they cannot come up with anything. This is good to have as a backup, and will probably give you peace of mind.
Remember with discursive, it is a mostly balanced discussion with personal anecdotes. That means your idea should be something personally relatable to you, and only you can form/decide this!
In English, the 'idea' per se is not the most important thing. Nearly any 'idea' can be a band-6 piece. It is more about layering the idea, considering different perspectives of the idea, and adding some complexity and sophistication to the idea that helps you achieve those good marks (as well as being able to actually write well, as the syllabus outlines).
Hopefully this helps!
Best wishes in your HSC