If you have any overlapping designations, all of the zones have their values set to precisely 0. You have to separate them or else they will be worthless. That's how it works now.
Is it a new behavior? Because I run a quick test in v50.03 and seems that wasn't the case.
I built two rooms separated by a single wall.
Designated the first room(including the walls surrounding it) as office and assigned to temple, checked value.
Designated the second room in the same way with designation overlapping over the wall and a different temple.
Re checked value for the first room no change.
Note that if two zones overlap over an empty cell, you do get a red warning in zone info panel, but this didn't change the value shown in the temple screen for me. Also note that this warning seem to update only upon zone change i.e. if build a door in that cell the warning doesn't go away, same if I designate over door and then remove it the warning don't show.
Engraved walls are actually only engraved on one side.
So the engraving doesn't add value to the wall tile only to the the adjacent north/south/east/west tile it was engraved from? If true, I wish there was an option to determine engraving direction.
I tried to run a test but either my fort was too new or my dwarf skill were shite because all my engraving added no value according to my noble