bump - I flew to SJO recently as a UA * G, and I went to the Avianca lounge in the international terminal. The lady at the desk initially denied me entry and said it was a first class lounge only.
On my way out of the lounge, I saw that they had a Star Alliance Gold symbol, so I went back and made my case again (told her I was Gold on United). She made a phone call to verify if I could go in, and eventually let me in.
The lounge itself was large and clean, and you got a ticket for 1 free alcoholic drink.