I bet if you compiled this into a small book(let) called "The Tiny Book of Web Design: <x> Tips to <pretentious verb> <pretentious adjective> Websites" and sold it for $5.99, you'd get a lot of buyers.
For example not all people will find "buttons" in your flat design when only difference is background colour, even if they can perceive the difference. Adding more "signals" like usage of icons, shadows, borders, fonts... makes the intent more obvious.
It's not about how to communicate with minimal amount of signals, but how to make the communication clear to greater number of people.
Joking aside, awesome tips.