This is being posted from a MTF perspective...
I think the importance of the whole passing or not thing is at least partially related to how introverted or extroverted the individual is.
I am a woman and expect to be treated as such. I'm also not ashamed of being TG. I pass as "Stephe" and feel I am a moderately attractive woman. I also feel I am "given the benefit of the doubt" in most cases and people assume I am female at casual inspection. I go by the rule "Use the rest room you are least likely to cause a riot using" and haven't caused one yet
I'm also a huge extrovert and really don't mind if I attract attention. I rarely have people use the wrong pronouns etc and feel I mostly blend into my chosen gender. But I have noticed people remember me and say things like "Hi, I remember you. We chat in the post office about a year ago and...." I'm sure they don't remember other people that were in the post office that day a year later lol. Or maybe they remember me because I am so extroverted and will strike up a conversation with almost anyone? Probably a combination of things. In any case I like I am "memorable".
On the other hand some people are VERY introverted and do anything they can to not attract attention. Even if they weren't transgendered. There is nothing wrong with that, it's just a personality trait. For someone like that, I can understand how passing can be critical to their happiness. I feel I am lucky I am not introverted AND transgendered! That is a tough combination to be.