> and when it comes to accessibility questions, the chief concern isn't necessarily whether everyone uses it.

I wish more developers had your perspective.

My Dad uses Windows' high contrast mode. It's less that "literal dozens" use this feature and more that this feature transforms all that desktop-shaped-material into a computer for the vision impaired.

Isn't the biggest performance enhancement the transition from not-working to working? I view accessibility as the ultimate performance enhancement for a given slice of users.