Seeing as I just spent 3 weeks in PR, I have some suggestions.
El Yunque is well worth the trip. Just keep in mind that if you're driving the exit to get into the park is pretty hard to spot. You'll see a sign, then you won't really see the little road that goes into the park through a small town. You'll say "this can't be it" but it is. Also, note that there are a few places to stop along the way to the main trail in the park. The La Mina trail is nice and you can swim under a waterfall. It is freaking cold, but lots of fun.
By far the most spectacular of all trails is the El Yunque trail. Keep driving along the road and you will find it, it's the most developed stop. It's about 4.5 kms
(or miles, I can't remember
) each way. Bring good hiking boots because even though there's a trail, it's quite wet and rocky at times. I rolled my ankle a couple of times
(without hurting myself
). There are moments along the trail where you will literally have breathtaking views.
Old San Juan is pretty nice, but I would spend a morning or so there. El Morro was quite nice, but going to El Morro AND San Cristobal is redundant.
For supper in Old San Juan, try Aquaviva. Seafood, cool atmostphere. Dinner for 2 including drinks and tip, around $100.
I spent a weekend at El Conquistador resort near Fajardo. It is beautiful. The nice thing about it is that they have a private island for guests only with a water taxi to shuttle you back and forth included in the price. Not cheap
(about $400 per night
) but you might be able to find a deal.
Fajardo is only about 40 minutes from SJ, so a day trip is feasible. A guy I know did a "booze cruise" on a catamaran the "Spread Eagle 2". He said it is great. Snorkelling on reefs and pina coladas to your heart's content with a BBQ lunch too.
That's about all I can think of right now.