Worth also looking at other airlines for the North American-SJO hop. You won't be able to earn/burn BA miles but it will give you more flexibility.

Continental are good (better than AA imo) and IAH pretty simple and straightforward to connect to. Often an easy redemption if you have some BD miles tucked away.

TACA (a confederation of Central American Airlines) serve most of the major hubs in the US, are safe, reliable and often offer very sharp fares.

Lastly, AA (and CO I think) fly to Liberia in CR which might open up some other journey options.