L.B.
My husband and I have been to Puerto Rico 2 times. Both times we spent about a month. I have a friend that owns a home in Las Marias which is on the other side of the island compared to San Juan. I think that you should try to tour as much of the island as you can. Rincon is on the other side also and it is beautiful, the beaches are fantastic and are known to surfers as having great waves. I think the salt mines are in that area also. You will have to visit the rainforest, I think the name of the town is Las Llamas or something like that. Definately try pinchos, they are like shish kabobs and are sold on the side of the road - they are yummy!
The roads are narrow and windy and along mountain cliffs and they drive like crazy over there so be careful
I highly recommend that you visit Culebra, it is a little island in Puerto Rico, I think that you can take a little 4 seater over from Old San Juan, it takes about 15 minutes to get there and it is worth it. Culebra is not very crowded with people and it is absolutely beautiful with the most beautiful beaches with white sand and clear turquois water and beautiful bluffs to tour.
Also, make sure that you see a cocqui, (probably spelled wrong) it is a little frog with suction cups on its feet that climbs the walls and sings "cocqui, cocqui", it is very cute.
Have fun!