Fred,

Definitely visit Old San Juan one day - take a bus in early one afternoon.
Walk around, shop, visit the old fort if you're into that stuff, but check out The Parrot Club

http://www.tripadvisor.com/Restaurant_Review-g147320-d786715-Reviews-Parrot_Club-San_Juan_Puerto_Rico.html

I've had a couple of meals there and they were memorable - not fancy gourmet (or particularly expensive), but a cut above - it's one of my dozen or so favorite restaurants anywhere!

If it's late in the evening when you're done, consider taking a taxi back - I do not know when (or if) busses stop running.

Enjoy!