I have the same issue with figuring out how in depth my explanation of the areas of study/debate that I would like to pursue should be. I am applying with a BA, and I'm worried that what I have so far is really broad and not exactly novel (I need to learn more about what has been done in those particular fields of discourse before finding untouched areas, as you have been so fortunate to discover). I feel as though I have to do so much more researching now just to be able to write my SoP....