> , maybe a collector craft could approach and collect several targets on a low Δv budget? It's not something you could do manually, but space has also this nice property that you can predict trajectories accurately far in advance,

So, the issue is, in the low orbit environment there's no kinds of slingshot or other maneuvers available. You need to match height of the orbit at a point, and need to at least coarsely match velocity at that point, which means you're basically in the same orbit as the object. Sure, you can play games with slowly matching phase, etc, but the delta-v requirements are simply inherently high.