The  East Egg is a place for the rich but in the comparisson with that of the West Egg they've achieved their position and wealth inhereting fortune from their ancestors. So they may be called ARISTOCRACY. Tom, Daisy, Jordan belong to that layer of society. At the same time people could "earn" significant amount of  money no matter legally or illegaly. They are called NEWLY REACH  and to those belongs Gatsby . The disticntion of rich people gives us a feeling, that aristicrates will never fully  accept the  newly rich to their high class society in spite of the  possible profit from the cooperation.
Remember that thought, we will discuss it letter, talking about the  American Dream. 

It occured to me that an egg symbolizes the beggining of life and it is not yet clear what will appear after it cracks. We see just  a cover and just suppose what is inside. But we can never be sure. It may turn out that there will be a chicken or a crocodile, or even nothing.. it may occur to be rotten . That is the idea of Fitzgerald:  all the representatives of the upperclass society despite their luxurious and glamorous way of life, their monumantal castle-like houses, expensive cars and mind-boggling clothes of the latest fashion are in  the highest degree corrupted.