It's definitely appropriate.
> This again makes presumptions about what kind of site you're building.
It doesn't matter whether you're building Facebook or the site for the window cleaner two doors down the road; you never want issues with maintenance, ever. Make sure you can move a person's wall post to a new location without issue, make sure Bob the window-cleaner can move a testimonial from the footer to the sidebar without issue. Size of project is wholly irrelevant.
> Specificity is an important part of the cascade.
It is, and an ID is the quickest way to f#&k with it. As is qualifying your selectors. You're tying yourself to commitments that you might not want to keep.
The things you are arguing against are the most fundamental in helping build maintainable websites.