There are some Meta questions that were relevant during private beta, but do not apply now that we are in public beta. For example, Do you know more experts? refers to the invitation box that appears during private beta, that no longer exists now that our site is public. This means following the link leads to the public main page where there is no invitation box.
Should such questions be deleted to avoid confusion for new users, or is there a reason to keep them?
No, we should keep them.
Just because a question does not apply to our current situation anymore (whatever this may be), this does not mean it can not provide value to others.
As an example, other upcoming sites may (and will) face the same or similar problems that we also faced, and keeping these old questions around may provide valuable information to others how the problem could be solved.
Another example would be all the bug reports on Meta SE. Hey the bugs are fixed now and some were fixed years ago, but the questions are still around and everyone can look back.
Just recently I read something about flag weight. I was curious what that is and found information that it happened to be removed long time ago. Nevertheless I still found information about how it used to work, how it was calculated, etc.
Back to your question: If such an old question becomes a problem, we can still close them or add a status-completed or something to the question. But we should definitely leave them available for others to read.
