While scientific approach would be nice, it is hard to do, and even harder to do correctly in the way applicable to the specific situation. And in the absence of the research, all we have is intuition and anecdotes.
And they work both ways -- there are anecdotes that making code beautiful leads to better outcomes, and there are anecdotes that having ugly code leads to better outcomes.
This means you cannot use lack of scientific research to give weight to your personal opinions. After all, that argument works in either direction ("There is no evidence that leaving duplicate code in the tree leaves to worse outcomes... A true science would provide...")
