Here's something worth waiting for – a delicious meal for just $4.30 (7,50 reais). There are fancier places where you can get yakisoba in São Paulo, for sure. But not only is this a treat, it is also an essential element of authentic São Paulo atmosphere.
I don't usually recommend eating food from street vendors in Brazil. The Liberdade fair is an honorable exception because it's very traditional and closely monitored by health authorities; the food is made fresh at very high temperatures and sells very quickly. Even so, I suggest you read these traveler's health recommendations.