Glenn,
In my area, the rule of thumb is, if half of the wall surface area of a room is opened to framing in the course of a remodel, the room is required to be rewired to be compliant with the current NEC. In a dwelling, this is applied on a room by room basis. It's felt that at 50% or more, the extra wall patching caused by the additional wiring doesn't add that much more to the cost.
There aren't many slab on grade homes in this area which helps minimize the number of truly difficult homeruns for the bath outlet circuit.
