As for San Blas... it's a great place. We've seen lots of Americans here. Many have chosen to retire here. The town is very old and is built on an esturary. River translates to mosquitos and no-see-ums, so we try very hard to be back on the boat 2 miles offshore by 4 pm. 
One of San Blas' claims to fame is that Henry Wadsworth Longfellow wrote his last poem "The Bells of San Blas" here. We visited the ruins of that church yesterday.
We also hired a panga (open boat) to travel far up the river to its strat at Tovara Springs.
At the end was an artesian spring and pool of water where we swam. As we were leaving the pool, we heard and then saw a huge crocodile maybe 15 feet from the spot we had been swimming! Needless to say nobody had been aware of his presence minutes before. What a shock!
