First off, your devotion to detail is pretty cool! If you're going to be spending a lot of time in that city, I can see the value in taking the time to model the entire city. Of course, if that city's just a small part of the world of your comic, then the time spent is still valuable, but it'd be more than what I'd want to spend.
Background detail can be a great tool. With it, you can set hints to foreshadow future plot elements or re-enforce theme and atmosphere. It can help immerse the reader in the world of your story. Of course, sometimes, you have to let the background go to emphasize some important emotional or physical movement in the foreground. Our art's pretty detailed in Atonement.
We take a lot of time painting the characters, most of all. But there are also little details, like the effects on the floating screen in panel 1 above, or the reflection in the broken visor on panel 2.
But sometimes it's nice to really develop the background of a page, whether that's a sprawling cityscape or a bar full of diverse characters each with their own story. There are a lot of ways to <3 detail, from the story specifics, to little clues in your art (showing vs telling), to doing what you've done and designing an entire city!
I think there are some important things to ask yourself when considering details for your comic, too! Like, "Okay, cool. I've imagined this incredible, rich world. How to I communicate that depth to my readers? How do I make it matter to the story? How do I do those things in a way that's immersive and not forced or confusion?"
If you've gone far enough to develop this amazing mythology in your mind, make sure you go a step further and think about how you want to effectively share that with your readers! It sounds like a no-brainer, but I hear from folks all the time who develop a mythology and then pretty much skimp over any opportunities to express the depth of their world through their storytelling.