Wow you're moving fast! You already have a reduced prescription, got books, etc. That's fantastic.
And you are more aware of your vision. Even better.
When you view the stereograms is it just wrong on the edges? I think the closer to the edges the harder it is to see the picture. That's the way it is for me. Sometimes it's the artist as well. Some artists like to put tons of 3d images and clutter it up and it's difficult to view. I found one artist to be the best and I enjoy viewing his art because it's easy to see. His name is Bohdan Petyhyrycz. The book I have is called Another Dimension from 21st Century Publishing but they don't publish it anymore I had to go online and find it used. You can get it used for a few bucks. Search on addall.com for it.
It could be one eye working less than the other. Is your prescription very different between the eyes? If they are about the same then I don't think that one is working less than the other. From what little I've read about it, it seems that one eye will be significantly weaker. But then, I don't have experience with that so I don't think I'm the best person to answer that.
Your attitude towards life may have an affect on vision. I think the jury is still out on that one. I don't doubt that it could, but it's difficult to be objective about it. I've read about it from others but I never made the connection myself. Play around with it and see what you come up with.