Poor Little John can't even afford the $4000 one way ticket to China. If he can afford it he would struggle with affording the return flight. The fixed costs John must spend on his flights already eats up the cheaper Chinese accommodation, food and consumer goods.Your John Smith could only afford a trip to China if:
1. He could find a McDonald allowing him that many hours per month. And
2. He would have to sleep on streets and eat from dumpsters for the full month to save for the trip.
In addition to the tickets, he would have to pay for a shower, a haircut and/or a shave, some clean clothes, and a ride to the airport.
Let's say after all these he would still have about 1000 dollars left for his spendings in China. Yeah with that much, he could probably have the "80th+ percentile" lavish lifestyle in China for a week at the best. Then he would have to go back on the streets of California.
See what's the flaw in your hypothesis? Your John Smith would have to survive first at home before he could pretend being a lavish "80th+ percentile" person in other countries.
But John probably doesn't think about China or exchange rates or arbitrage. John just wants to pay next months rent, his car lease and his credit card debt. If he can't pay off those obligations, it is unlikely he would go to China. For a hypothetical John to travel to China, he must be secure via homeownership, and jobs. Say, a $100k a year financial analyst. The problem with such Johns is that since employment is precarious, he cannot risk spending more than a week or two in China, which is not enough to deprecate the fixed costs of plane tickets. Unless you make even more or have access to cheap transportation, arbitrage in China is still difficult to achieve.