Egypt is a situation dictates only strategy just like Sea Lion IMHO. I prefer either or both at the same time, but I never rarely spend for them.
Sea Lion:
For example, a typical buy for me G1 is 6 artillery/2 infantry or 5 artillery/1 fighter (if the UK bids a fighter to Scotland). This G1 buy doesn’t scream Sea Lion, but, if the UK player doesn’t spend much on London, well guess what, Germany has some options especially if other battles went right for Germany like SZ106. I don’t like to buy an aircraft carrier G1 even though Sea Lion is always my Axis fantasy. In a Sea Lion game, I buy the Carrier and maybe a destroyer the same turn as Sea Lion and place it in the channel on G3. Also, if doing Sea Lion, Germany needs a tremendous amount of ground units in order to properly manage Russia.
Cairo:
Just as Germany needs to a lot of ground to manage Russia in a Sea Lion game, so to does it if Germany spends on boats to get Cairo. If Cairo is taken by Germany through the spending of income on boats, I think a smart Russian player might have the chance to get NOs and become very strong in their own right. Anytime that Germany spends on boats like a G1 carrier purchase, Russia can to make lots of aggressive purchases.
I think it best to get Egypt with Italy not Germany and only under the right conditions…mostly achieved through poor dice on the part of the UK while good dice for Italy with minimal help from Germany. Otherwise the bite is not worth the squeeze IMHO. Also, if Italy is the one that gets Cairo and gets to place an IC there, then Italy actually has it’s own purpose besides the important can opener role.