I haven't drawn that many characters in masks or whatever else that might cover up their faces (and I'm pretty sure I don't have partial face-blindness either), but I totally agree on what you say about playing with faces and identities.
I have been working on a long form comic where gas masks were going to be used on several individuals, both as an important part of the story line, but also due to themes about identity/personality/sense of belonging/understanding of existence. (Wow, I make myself sound really deep). It's currently under reconsideration though, because even though I do think gas masks are super cool, it's one of these things that can get a little old when used too frequently, so we'll see.
Anyway, I think that in terms of character design, accessories like that can play an important part. One of the things I remember best from working on character design, was that your character should be recognisable even when presented only as a black silhouette. Things like gas masks, scarves, etc. can help make your characters more memorable and help them stand out.