Well the immediate effect would be bad, but it might be better in the long term - how can it possibly be any good that an entire population in a territory is dependent upon government subsidies? It would mean that there are too many people or they aren't being productive enough. It's a situation that would be vulnerable to even the slightest changes - rather like the situation whereby most of the third world/developing countries today are net importers of food (that situation was just trouble in waiting with food prices rising now due to mainly to rising fuel costs and food consumption (especially meat), not biofuels really since corn and wheat biofuels would never affect the price of rice which isn't made from corn or wheat and isn't used as a biofuel).
One effect would be that a lot of residents from American Samoa would probably end up migrating to the USA before and after any such cession (which would be good since it would ease the population pressure).
Another is that all those American Samoans who played American football might end up switching to Rugby Union and some of good ones suited for rugby union might end up playing for Samoa. Of course plenty will probably still end up in the United States on American football scholarships or may end being contracted for teams there.