If you are looking for nice beaches, the nicest ones within a reasonable distance of the cruise pier is at Isla Verde, right near the airport. I would siggest that you call the El San Juan Hotel and inquire if they have a day pass program which would allow you to use the facility and beaches, and maybe have lunch at a fixed cost.
You may also be able to do this for the Wyndham El conquistador hotel and spa, which I have not seen, but I'm told is just gorgeous.
A little further out is Luquillo Beach - kinda funky, lots of places to eat. I am not a fan of the Condado area, especially their beaches.
Check out the show at the Wyndham El San Juan. They used to have a great flamanco show, and other top name entertainment acts. They also have a beauriful casino there if you're into that. It's like the old ones in Monte Carlo