The US policy towards Cuba was very welcoming towards refugees from the island.
Between 1975 and 1997 the US took in 1.3 million people from Indochina. What if President Nixon opted to open the floodgates with regard to Indochinese migrants, seeing the refugees as "good anticommunists"?
One interesting tidbit is that most Hoa (chinese in Vietnam) went to China historically. They controlled most of the businesses in Saigon and were a very very successful and entrepreneurial demographic in the country. If they largely went to the US, they could have a very positive effect on the US economy.