Is a tree/graph visualization of methods literature a useful addition to lit review?
I'm a little bit cautious about diagrams like this. The reason is that often the relationship between different pieces of work is much more messy and partial than is readily captured by such a diagram, and systematizing onto a diagram can cause one to unintentionally leave out or "neaten up" some of the most interesting pieces of hybrid work.

That said, sometimes diagrams are appropriate---consider, for example, some of the wonderful diagrams for relationships between computational complexity classes.  In this case, a diagram is a wonderful aid to comprehension, and as such, if the work in your field really does organize so nicely, I think that using a diagram is a good use of space, particularly in a document like a thesis or thesis proposal where you are not facing tight space constraints.