Capt Undies,
I am sure you are not suprised to learn that the dissimilar goggles piece was quite contentious at the working group meetings. The example Delta Tq uses, and feelings that were similar to yours were expressed and defended, however to date, there has not been a safety case mounted against using dissimilar goggles. On the flip side, there were several cases put forward in support of the current wording.
It was not felt practical at the working group level to create a hierarchical list rating the different models, but to refer to the gain, resolution and acuity specs as the primary driver for what would be considered "higher level" NVG. In addition, the operator is compelled to rank the NVG in the Ops Manual, and must therefore present a case for this ranking to be reviewed by CASA. The operator must also do a specific risk management appraisal, and develop procedures when using dissimilar NVG.