Much of UX design is suck. People can't tell a difference, not at least in detail. If I were to change color of a button, maybe you'd think no one cared.
But such things do make a difference.
But such things do make a difference.
If one were to change a button from red to a slightly different red, which is a detail, then most will not notice nor care. Change it from red to green then there could possibly be a change in response; be it good or bad.
Of course the most perfect site won't save crappy content, but the ugly site's content may never be read. It's similar to all the non verbal clues in human interaction. The tone of your voice and even the color of your shirt do make a difference.
I'm just saying that changing from one font to another that are almost identical, and to the layman are identical, will not have much impact in the long run.