Are the "about" and "faq" links in the header really necessary for those who have some reputation on Stack Exchange sites? Maybe they should be hidden for users whose reputation is at least, for example, 100 to free some space for more useful links.
For example, someone could have answerd 1000 questions gaining 10k reputation, but he could never had used meta. Reputation means that someone is expert in the topic of the site, and not the expert in the site mechanics.
I quote the FAQ at least once per week, and sometimes several times per day (on bad days). It's still the most useful link on the site for me, I can't think of any reason we should remove it or make it less visible. Even on Programmers, where I'm a moderator, I can't think of any link more useful than the FAQ (although the delete button is a strong candidate, but it's more of a button than a link).
The about link it's a bit meh for higher rep users, but it's moved on the footer when you are logged in anyway, so...
As 20K user, and as moderator, I find myself quoting the FAQ when answering to question on a meta site. In the case I am proposing a change to the FAQ, I would need to first verify the change I am going to propose has not been already implemented. In short, the assumption that high reputation users don't need the link to the FAQ is wrong, IMO.
You are also making the assumption the FAQ is never changed, which is not true. Stack Exchange developers can change its content, and the part titled "What kind of questions can I ask here?" can be edited from the moderators of a site, to add a new category of questions that can be asked, or that should not be asked. 20K users needs to see that list even if they are using the site when it was in its private beta phase; if they don't need it to know what type of questions they should ask (because they answer questions instead of asking them), they still need to see it to see if a question asked by other users is on-topic, or welcome.
To make a comparison, it would be like not showing the "privilege" link to 20K users for the simple fact they have already all the privileges. Also in this case, a 20K user could still need to refer the privileges page to see if something changed in the privileges, or to report an issue about those pages. With the privileges page on this meta site, there is also something else to consider, that is not valid for the FAQ: The privilege pages are Community Wiki pages that can be edited from 20K users, and can have suggested edits from other users.
If the request would be to show the FAQ link only when something has been changed, I would be contrary, for the fact a high reputation user could need the link to the FAQ in any moment, for example to suggest a change to the FAQ.
About the "about" page, I don't normally read it, but there is still information that can be useful, even it's not information that somebody keeps looking for: the list of appointed moderators, which includes also the date/year they have been appointed/elected.
The fact the "about" page is not so frequently accessed is probably the reason the link is not on the header, for users with a reputation higher than a threshold. Yet, it's not a static page, and it is subject of changes as any other page.
The list of the moderators is also shown in its own tab of the "users" page, and the links to the "faq" and "about" pages has been replaced with a link to the Help Center. Still, what I said about the FAQ page is still valid for the Help Center.