Now I know this is a very much debated area, the whole area of "how do you measure legibility" (of which http://typophile.com/node/41365 is a great thread), and the fact that aesthetics are subjective (as I believe is legibility to a point - reader preference, familiarity, etc.).
What I am looking at, is if the conducting of legibility tests, followed by subjective aesthetics tests (in which various samples would be created with varying levels of creative elements and the same tests applied as in the legibility studies as well as preference, etc.) to see if it is possible to find a balance point between the two. The theory is that if you can find a point where the legibility is maximised, and then find the point where the aesthetics don't negatively affect the legibility, then you can effectively improve the reader experience.
My thought behind the possible application of this is in uses such as study materials and required reading. For example if you can increase the aesthetics to a point where they are maximised without decreasing the legibility of the text, can you in theory improve the reader experience, and would it have an additional effect on other aspects; retention, comprehension.
I know this possibly sounds a little vague, but I'm really interested in people's thoughts on this.