Manxman , I'll try to offer up what litle help I can. First of all, as you know, your likes and dislikes may well vary from mine---- I'm interested in history,the people and culture of the places I visit, etc.
That being said, we have done that cruise twice--once on the Coral Princess and once on Celebrity--with the exception of Cartegina , Columbia.
The Coral will enter the locks at the canal, then sail into Gatun lake. Those taking tours will be tendered a short distance to their respective meeting places.
At Panama on the Coral, we took the tour to the Embera Indian Village. This consisted of a bus ride, then a ride upriver in a motorized dugout canoe to the Village. We were welcomed by the chief, served fresh fruit, wandered around , took photos, watched and participated in a dance, etc. I loved that tour and really enjoyed it. The Indians have handicratfts, such as baskets, bowls, etc. for sale. The Women for the most part are barebreasted which is no biggee, as it's their way of life. If you enjoy meeting different cultures, etc. this would be a great tour.
There is a tour to a REPLICA of an Indian village so if you want to see the real thing, be careful that you carefully read the tour descriptions
In Costa Rica, we took the bus tour to the Capitol of Costa Rica, San Jose. It's basically an all day trip . You get to see a lot of the country and get to tour the capitol city. Lunch is included. Again, I loved this but you may not like the same things I do.
I have been to Aruba a couple of times and have done an island tour there once and just spent time around town the last time. Aruba isn't that big and is very dry---looks like the american southwest with brush, cactus, etc.
Haven't been to Cartagina so can not offer up any help there.
The second time we did that cruise was on Celebrity. In Panama, we took the train trip across the isthmus alongside the canal to Panama City on the west coast. It was very nice--- the train was smooth, quite, had a/c and bathrooms. There are platforms you can stand on outside between the cars if you wish. We spent at least half our time standing there and now and then snapping a photo of a ship. You will stop at the locks on the western side to get a view of ships entering / leaving the canal from that end.If you should decide to do that tour, I would not advise spending the extra money for a " domed " car, as everything you want to see will be to the side, not up through the glass roof of a r/r/car.
Second time in Costa Rica, we took a tour that included a boat ride on the Toutuego canals, then a ride on a converted sugar train and lastly a bus ride with a stop at a banana processing facility. That was a great tour also.We arrived back at the dock in plenty of time to go to the shopping area near the dock and crossed over to the town area briefly.
I would visit Princesse's website to check out their various tours and try to match up with what you are personally interested in.
I would urge you not to go wandering around by youself in Panama nor Puerto Limon . In Puerto Limon, there's a shopping area near the dock. You can go through a gate at the back into the town area, which we did but we didn't go over block and there were a lot of other cruisers around that area so that small area seems ok-- other than that, I would not go wandering off anywhere.
Hopefully this has been of some little help to you. I have always wanted to go back on the Coral and have always wanted to go to Cartegina so maybe someday I'll make it.
Lots of luck and smooth sailing. :wave