"Worth it" is such a totally vague and subjective phrase, and totally a personal decision. We can't calculate that for you, we don't know you.
Easy for us...we would almost always chose the longer cruise, and given the dock is less than an hour from our house, very easy to chose to cruise from SF.
What do you define as "short"? That could be 3 or 4 days, but the number of those cruises is small.
Probably the better place would be somewhere like Ft Lauderdale or Miami.
Start by joining your Roll Call, here:
https://boards.cruisecritic.com/forum/228-oosterdam-roll-calls/
Some research on the Ports board would be good as well:
https://boards.cruisecritic.com/forum/47-south-america/
Interesting getting advice on SF transit from a New Yorker😂.
BART to downtown will work fine. However, taking a checked bag on the F Trolly is not allowed. Those are historic trolleys, and very small inside. Even two checked bags is going to be crowded.
I would suggest taxi or Uber from your hotel, unless you are fully mobile and able to drag your bags. Walking on the Embarcadero is easy, its a wide, flat walkway. But dragging bags might not be fun if you don't have the mobility.
Yep...Venice would work.
And, just so you know, the ship docks in Livorno, 90 minutes away from Florence, each way. You might consider doing excursions to other locations from Livorno, and spend a couple of days actually in Florence on your land trip, knowing in advance you are doing your land trip.
First of all, to stay in any medium to large city in Europe, you don't need to speak the local language. Discussed here frequently.
You could spend many days in Rome easily. But a good idea would be to spend 3 nights in Rome, then train to Florence for 2 or 3 nights.