If they solely look for and record sightings of specific plates associated with active investigations? Not a lot, no.

The core problem with Flock is that it tracks innocent citizens on the off chance it helps catch a criminal, when it could be designed to only track already known wanted vehicles.

You are committing the scale invariant fallacy where two things are the same if they only differ by scale. A chance encounter with a human who reports the sighting to be investigated isn't even surveillance, your massively watered down flock still turns a bolo into 24/7 surveillance of the vehicle going forward. Which if we use the test of could humans do this it would at minimum require a warrant.