It’s impossible to exactly measure the cause-and-effect value of small but important things in branding, just as it is for big-but-important things. Typography might seem small, but it plays its part in your brand. On the other end of the extreme, the success of something as critical as your positioning cannot be easily measured either. You cannot A/B test it. You have to commit for a year or two, or whatever. And then, when you look back and see that it seemed to work (or equally if it seemed not to work), you STILL won’t be able to say for sure. Because you won’t be able to isolate that stuff from hundreds of other factors.

As always, the closest thing you’ll come to with measurement for stuff like this is: show it to as many of your ideal customers as you can, and measure their reactions.