Beagle,
As being someone who taught the first Navex in a similar fashion to your method I whole heartedly agree that this appears to be most satisfactory way of training.
All training should be seen a series of building blocks and the first Nav should be viewed no differently.
I considered that an important part of the first navex was an extensive pre flight planning. This planning not only covering the obvious such as correct plan, equipment, but as to what to expect during the whole flight, from submission of the plan, radio calls right through post flight requirements.
To this end I also found that a "virtual nav" from the comfort of a couple of chairs in the briefing room to be beneficial.
This "virtual nav" would cover siting in the "virtual aircraft", organizing charts and equipment, departing from the area, making appropriate radio calls, conducting enroute nav techniques and other checks in the appropriate places, returning to base etc.
Then on the actual navex I would unload some of the workload pressure.
I would make Nav 1 a three leg exercise, with the student flying the first leg (something he is used to and comfortable with) whilst I would complete all else such as radio calls, G/S checks, Nav Log notes etc, advising the student as to what and why I was doing.
The second leg was role reversed with me flying and the student completing the navigation items, radio calls etc. These items supervised and prompted as required.
The third leg would see the student have a go at putting both the navigation and flying together to get a feel for the workload. This being by no means a test, but a dual exercise as a prelude for Navex 2.
During the flight the student was encouraged to enjoy both the view, scenery and the flight itself. An appropriate work cycle should be developed to this end allowing the student to realize that it is not necessary to follow track on the chart every second of the trip.
Teaching of basic map reading were included during on all legs and Airmanship points were reinforced.
Regards