Since our big economic crisis, I think we can find all three of these today. Looking at the East Egg people, I would say that the Wall Street people who have been taking in these huge bonuses, while a huge chunk of the country goes without jobs, would represent that side. They all have been living a certain style of life with fancy clothes, fancy homes and fancy cars. Some send their kids to boarding or private schools. They continue to live this lifestyle, even though many are going without jobs at all.
The West Egg people, who are conservative and moral, have had to cut back on their spending. I think even the White House now could fit into this scenario. They have cut their spending down to about 1/3 of what Bush had been spending. The Obamas have even brought the mother-in-law in instead of hiring an expensive nanny or teacher. That's one way of cutting spending and using what resources are available. Other West Eggers would be the men and women in the business world who still have their businesses, but are taking the cuts in salaries along with their employees.
The Valley of Ashes belongs to the families who have taken the hit from the economy and can't seem to get back into the working force. They are losing their homes and have to draw on unemployment. They've been dumped on by the East Eggers and can't do a thing about it.
East Egg, West Egg, and the valley of ashes are locations separated by class and income in the book. Fitzgerald was showing the reader how completely separate and isolated each of the classes each locale represented was. In many places, this separation still exists. People today, in many locations, try to be politically correct and cover up those differences, but they definitely still exist. The East Egg residents in "The Great Gatsby" were the old money rich; the families had been wealthy for generations. Those people are still there and probably, for the most part, travel within their own spheres. West Egg was for the newly wealthy people or the people closer to middle-class incomes. Today, I believe there is more mixing of the East Egg and West Egg types because enough money will buy a person a home anywhere he wants to buy. Not being an "East Egg" person, I can only guess that old money still tends to socialize more with old money than with new money. People with money generally become friends with other people with money. The valley of ashes represented the desperately poor people who would never climb out of their pit of poverty. Sadly, we still have those people, too, and they do not interact much with the other two classes of people. What Fitzgerald didn't show much of were the groups of people between the West Egg types and the valley of ashes types. Those are the categories most people fall into.