Here are the pics of the bookcases as promised. You can see how I added wood to the bookshelf on the left. On the second unit, I drilled directly into the bookshelf. That one seems to be more stable since I was able to get closer to the edges. I'm going to redo the first one.
I bought handles to add to the sides of the bookcases. I'm then going to stack them against the wall similar to how the bookshelf with the paint is. I'll put labels on the end like you'd see at a library, so I can identify what's on what shelf without having to pull the bookcase completly out. Simple solution to a storage problem!