I definitely agree that having a good understanding of git's internals is a must for using it to its full potential. I'm not sure you have to go as far as implementing it yourself, but it is a sure fire way to get there. For me it didn't all click into place until I understood the data model behind git[1]. A git project is just one big DAG of objects, and each object at its core is either a blob, a tree, or a commit. When you understand that, you can start to view every git command for what they actually are, a sequence of operations on this data structure.
[1] relevant xkcd: https://xkcd.com/1597/