Answer:
They got the chance to fly the latest in modern jets; MiG17s, 19s, 21s for the Northerners, and A1 Skyraiders & T28 Trojans (propeller driven), plus F5 Freedom Fighter jets for the Southerners.
Although probably a joke the answer above contains some truth.
During the war the North was only supported militarily by the USSR, while the South was financially supported by the US government and the US service men spent a lot of money there. After Januari 1973, however, the US Congress stopped most of the financial support.
After the South was conquered by the North in 1975 Vietnam became economically isolated from US support. Because of financial problems the USSR was not able to support them either.
So after the war Vietnam did not benefit from the war. Like the Korean war it just was one of those great tragedies of the Cold War.
Vietnam received over ten years worth of military knowledge/equipment/training and civilian related exposures such as shipping and receiving (import and export) experience)/medical/engineer/food/educational benefits from the US during the war.