But if you've got a snapshot once per day, times ten days, and this kind of aggressive search function touching every file? Maybe an extra 1-2G of metadata being pinned

I don't follow. If you have one master copy and 10 snapshots, and you change the metadata on the master copy, why would it generate more metadata (than when having a single snapshot)? All those snapshots can share the same metadata block (provided the file wasn't changed in the meantime) and just the master copy would get a new metadata block. So it should be the same amount of newly written blocks, regardless of how many snapshots you have. What am I missing?