Here is my personal opinion of the Panama Canal Train excursion. If you like nostalgia and want to spend $100 to $150 then go ahead. If you want to see the canal and really
learn something about the canal zone don't bother.
I found it a complete waste of my time. I LOVE
trains but you go to the canal to see the canal and the train speeds along at 50 mph and you really miss most of the canal. The bus tour at the end is boring and non-informative. It was nice to ride on the railway that help build the canal but that "mystique" wore off in about ten minutes. Plus the delicious box lunch of was a joke.
(Remember this was the "Executive, Dome" car that advertised a delicious lunch. It was a box with an apple, some sort of juice box, and I think a cookie and I can't remember if there was a sandwich.
If you want to experience the canal; either take a full transit or take an ocean to ocean excursion in which to take a boat from one end to the other.
In regard to the OP's question: I find that many folks do what feels comfortable for them. If that's what they like then go for it. I personally find that I am burned out on the Caribbean and unless the cruise is for the people or the ship then I have really no desire to cruise there again. Living in "flyover land" I have to fly to any port so it doesn't make any difference if the cruise leaves from Miami or London, I still have to pay for airfare.