Thank you all for your thoughts!
I will stay four weeks in Egypt and 5 nights or so in Cairo. My travel plans are still evolving and I must confess that I haven't looked at Cairo details yet. So I cannot already answer precisely what I want to see or not. Since most of you are experienced travelers to Cairo I appreciate your inputs vey much. And with any place my four weeks in Egypt and 5 nights in Cairo will never be enough to see and enjoy it all. But your inputs help.
Thank you!