Hi,
I have an existing layout that seems to work at 46" rail height, also I have not detected a hard height rule anywhere, not sure there are any rules really!! My own interpretation is that as a basic guideline the front fascia and back scene should enclose the visual space so that this is all that is seen - the book to some extent focuses more on controlling the presentation to exclude distractions (operators, hall surroundings etc) rather than fixing a height. Hence the height rather depends on fascia aperture, back scene height, depth of board and scene modelled.
In the "Cameo book" and at exhibitions O gauge layouts are I believe under represented in the "Cameo class", seems the P4/EM guys rather dominate, it would be good to see a few more 7mm layouts. I've always thought it ironic that if you raise a P4 layout to eye level then the visual benefit for the track is reduced - the birds eye pictures show it for sure but this is not how they are seen at shows.
As for the book, I found it interesting irrespective of the competition and has some useful ideas.
Steve