What struck me about your question was the nuances behind the word "visiting." Your question implies that Nick never intended to stay in the East, ... that he fullly intended to move back home to the Midwest. In this regard, I don't agree. Nick was escaping the Midwest and the trap of his "clan ... descended from the Dukes of Buccleuch." He wanted to MOVE to the East and not simply visit.
That aside, let's get to the meat of your question and look at his "incentives" from the text. Directly after Nick mentions how trapped he feels by being in his particular family clan, Nick talks about his great-uncle and his involvement in World War I. It is precicely his involvement in the military that Nick says made himm "come back restless." He expands further to answer your question directly:
Instead of being the warm center of the world, the Middle West now seemed like the ragged edge of the universe--so I decided to go East and learn the bond business, so I supposed it could support one more single man.
There you go. The charm of the Midwest has gone in the eyes of the more worldly just-back-from-the-war Nick. Most likely, he is sick of being around the same "blah" people with solid values. Nick is looking for something new, vibrant, a whole different way of life. Enter West Egg. Something new? I think so! Yep, "solid values" sure do go out the window, don't they?
In conclusion, the irony is that Nick ends up simply "visiting" the East, even thought that wasn't his original intention. The East was too corrupt a place for little Midwestern Nick. He moved back where he belonged, clan or not.