I do not mean this to be lessen the craft of typography (which I am certain that it is!): For me, typography/styling beyond the very basics of bold, underline, italics and so on feels a bit like an aquired taste. Whenever I engage with related contend, I hear claims being made like "A helps to convey X", or "B and C should not mix, else Y!" - and I don't doubt that these claims are true, but I wonder if they are true for a selected few who pay attention to such things, or to statistically average person. My gut feeling would be that there are handful of claims that provably help get a message/intention across to a big group of people due to a mix of convention and how our brain processes what it sees - and at least 3/4 of claims that would not show such effect.

One proxy to try to answer this question would be to look at what successfull advertisements use (not necessarily the ones that win prices, but the ones that drive up sales). Their advertisment media might have other qualities that might offset typography/styling sins, but they are more likely to be intentional about using typography/styling to get their point across.