(Sorry that took so long...).
You have done some very comprehensive research.
My feeling is that small amounts of spinach and kale are not dangerous, and in fact, healthy. The undoubtably most healthy and helpful diet change that you could have made was to change the diet base from seeds to pellets. I use Harrison's almost exclusively (http://www.harrisonsbirdfoods.com/). I like them because they are additive-free, organic, and generally very well-accepted.
The argument against kale and broccoli is that they contain 'goitrogenic agents' , which are substances that interfere with the normal production of a thyroid hormone and can cause damage to the thyroid gland resulting in 'goiter', or 'thyroid hyperplasia' (the same condition seen in 'Iodine deficiency'). And as you noted, spinach does contain oxalates, but they do not appear to be harmful if fed in moderate amounts.
Another helpful managerial tool that will improve their health would be the addition of full-spectrum lighting (http://users.mis.net/~pthrush/lighting/spectrum.html) if they do not have access to unfiltered sunlight year-round. The facility should like this addition because these bulbs are used for treating 'S.A.D.' (Seasonal Affective Disorder) in people!
The following are some of my favorite sites for avian diet suggestions: I am feeding 6 (2 greys, 3 amazons, 1 pionus), so I switch between their food presentations, depending on how much time I have for preparation. The other great project that you could start with your flock would be to have them 'forage' for their food (see the DVD by Dr. Echols available at the Harrison website).
Here are the diet sites:
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