For a lot of people, they know that super nimble spaceships aren't real, but they may have never thought about asteroid belt density. People often see something in media that seems plausible, and assume that's what it's like in reality, even if the media portrayal was way off. I can guarantee it's happened to you at some point.
For an example in our own system, see Saturn's rings.
The aftermath of a recent collision between large bodies might be attractive to future spacefarers because it could expose the differentiated insides of planetoids in a convenient high-density but accessible form for mining. So it wouldn’t be entirely unrealistic for “future stories” to be playing out in these rich and dense regions instead of the space equivalent of the middle of a barren desert.
A statistically representative locale for a story on Earth would be in the middle of an ocean, but that’s not where most stories come from.
I do like the idea of prospectors diving into the debris of a recent asteroid collision to gather halfway pre-refined resources. With the rarity of asteroid collisions relative to human lifespans, I imagine the response the way deep sea creatures respond to a whale fall, sudden massive availability of resources. I might try to write that someday.
That's also an undesirable "area" of space for mining. A too-recent collision would be a dangerous area because of the excessive density. A "just right" area for mining might be a hundred thousands years old, but not tens of millions or older.
The terran analogy would be a volcano: Too soon and you're still ankle-deep in lava. Some decades later you have the most fertile land on the planet for your crops. A billion years later it's no different to any other part of the planet and not especially productive.
> whale fall
That's precisely what I was thinking of!
> I might try to write that someday.
I'd read that story! It's a ripe context for drama: the luck of discovery, the gold rush, the fight over the territory by rival groups, the "frontier" aspects and lack of civilized law and order, etc...
This doesn't seem like it should be a problem. The space miners don't need to jump straight to the middle of the debris field; they can just start at the very edges. The density of the debris field won't be uniform; it'll be spread out, even shortly after the collision. They can just go to the less-dense areas at the periphery, where it's safer.