Keep the Plaster or Tear It Out?
Keep it when the base coat is hard and the lath is sound, even with cracks running across the room. Tear it out when the lath itself is broken, or when the room is being opened for wiring anyway. We would say a few cracked walls never justify gutting a sound plaster house. And a hairline that has not moved in years, with nothing around it that gives when pressed, does not need us. Paper tape under a thin coat of joint compound will hold it, and paint hides the rest.
I had a friend I used to help with her home; she lived in an old house down by the beach. All of the walls in the home were lath and plaster. Most of the walls were in pretty good shape, but there always seemed to be some nagging walls in certain rooms that kept cracking, and plaster would fall off. In my opinion, if it was my house and I could not do the repairs myself, I would simply pay someone to keep fixing the loose plaster. Usually the spots that we fixed never came back; it was always new ones.