OK - so I took out all of my custom stuff and started with the examples in shared/classes/alfresco/extension. I moved example-model-context.xml.sample to example-model-context.xml and uncommented the my:sop stuff from web-client-config-custom.xml.
Everything but the my:imageClassification aspect fields show up as I would expect.
This is fine with me, I can just make my model contain the properties I need and not use aspects.
Should the my:imageClassification properties show up in Content Properties with the other example fields?