that's exactly what I'm saying

basically everyone uses Excel. And basically everyone is a MOUSE-first user (or, even further along the chain: TOUCHSCREEN-first)

keyboard-based menu navigation is not intuitive. it can be "poweruser" oriented, but it's not for most of the userbase

Keyboard shortcuts for those menu items are what most people will learn -- save, print, cut, copy, and paste will be the common ones that a lot of people will know.

I'd be willing to bet that professional typists and people who spend the majority of their day typing (email, word, IDEs/text editors, etc.) are the ones who will know more keyboard shortcuts and navigation, especially for the things they do repeatedly.

It really depends on how much you use it. If it's hours a day, you are a power user, and you'll learn the shortcuts. Otherwise it's annoying.