I'm using models that interact with each other with 100+ attachments and 30+ separators in Unity.
In my own experience, I'd say that you avoid changing the draw order of models in Spine animations. I only do that with 'individual' animations that I'm sure won't conflict with another skeleton getting in the way.
If you need to change the sort order of an attachment, I'd assign it its own parts renderer and set the appropriate sort value at runtime. Just my two cents on how I'm managing. Pharan may have a better solution.