As a teacher, I have my teaching resources stored in dropbox, which is synced to pdf expert, and I usually review my teaching notes for the following days on my iPad. I did this on an iPad mini, and am doing so now on my iPad Pro 9.7, and I find that sometimes, more pixels is just no replacement for larger pixels. It is simply easier to read on a larger iPad than a smaller one, despite the smaller iPad having a greater PPI. I imagine it would be an absolute dream to read on the iPad pro 12.9, but its way to huge and cumbersome for me to use in class at any rate.
I find myself annotating on pdfs a lot these days as well, and am contemplating picking up an Apple Pencil. I previously didn't bother with any because I found that they often weren't very good, but if the writing experience of the pencil is a game changer, it might help offset the inconvenience of walking around with one in the classroom.
The iPad is also faster and smoother than my iPad mini 2, and I guess that means less time spent waiting for apps and content to load. 128gb means more room for files. Will have to test if the higher res camera shows any significant improvement in scanning documents, and when using my iPad as a makeshift visualiser.