Our cruise only hit a few ports as well.
In Acapulco, I recommend going out to dinner to Su Casa restaurant. A gorgeous view of the bay and fantastic fish. I think they do lunch as well.
http://www.sucasa-acapulco.com/
Visiting the Acapulco Princess hotel is also fun.
Many people go see the divers at La Quebrada. While the divers are very good, their part of the show is not very long, and you have to put up with a lot of stuff just to see them. It's not a long taxi ride out there, but you get swarmed by street children trying to sell you things. Once you are inside, you pay for a seat that includes 2 drinks, which you will need if you have to sit through the dance show we saw when we went in October. If we weren't with a group, I would have left.
Most of the excursions through the cruise ship were not well received. People I met who just grabbed a cab driver and asked for a tour of the city did much better.
At Puntarenas, we went to Tabacon Springs, which was WONDERFUL! It was near the Arenal volcano instead of Poas, so we got to see two natural wonders. It's a 2 hour ride on bumpy roads each way, but I would go again right now if I could.
www.tabacon.com
There is not much to do in Puntarenas, so do consider an excursion. Many people go ziplining here, and love it. I was more interested in seeing the scenery in slow motion.
I have not done much in Aruba besides shop or go out to eat, but Frommers guide book has some driving tours that I would like to try some day. Oh, we did do a submarine trip as well. The reef is still being built up, but we did see a lot of neat sea life, and the guide was very good about explaining what we saw above and below sea level.