It is now on the list along with a discussion on the usefulness of the pursuit of originality and some sort of study into inspiration. The masters I'm doing in more practice based, so the dissertation is only 10,000 words, but that still obviously allows a lot of room for an interesting investigation. Your suggestions are great, thanks. I shall add them to the document!
To throw another wrench into the "Major-Happy/Minor-Sad" there's things like the use of Minor keys for other emotions, most famously the solemnity of Christmas in a lot of baroque works. You can also look at the modes, and their relations to happy/sad. Some of them sound more major, but sadder, and others more minor, but happier. Then you could look at how some keys used to have certain emotions/scenarios implied (some still do), and then you could look at how older tuning systems might have influenced that... Sorry. I get excited about this kind of thing.
If you want some cool shit, look into how harpsichords are/used to be tuned. It really emphasizes why people felt certain things about certain keys. because they were tuned to a "key", and weren't well-tempered, certain keys (like Ab in F) got REAL squirrelly. But even once they got into "well-tempered" tunings, they still use some interesting and weird tunings.