Can't answer number 1, however #2 no reason to swap them out, if they are working, you will replace a working system with another working system.

The only issue is the controllers for the isolator, and the testing that they do.
However that being said if the boat side breakers are tripping that isn't good. With a boat of your "vintage" you should have standard 30A breakers for the shore power entry points on the boat. The only reason(s) that they would trip are over-current or going bad (17 years old?) The fact that the marina has changed out to GFCI's on their end you should be tripping the shore side breakers not the boat side breakers.
Here is the simple diagram:
BIG MAIN BREAKER FROM DOCK --> Dock side breaker (NEW GFCI?) --> Dock side shore power cable plug --> Boat side shore power cable receptacle --> 30A Breaker on boat --> Cabin main breaker --> misc items breakers etc...
With the promarier monitoring system powered up it will cause a ground fault upon powering it up and every 4 hours after that. That won't trip a standard breaker, but will trip a GFCI breaker, as that is exactly what they are looking for at approx 5mA of current. What this does is test the path through the actual galvanic isolators to make sure they aren't broken. If the ground wire came off of them or it broke the GFCI test couldn't work. This would also light up the "FAIL" light in the small panel for the system. However if its working correctly it would trip out the GFCI breaker on the dock, which you would loose power right away and the system wouldn't be powered up any longer...
So if you are tripping the boat side breakers where the cables plug into that isn't good. If you are tripping the GFCI breaker only 50% of the time that isn't good either, it should be 100% of the time if the monitors are plugged in and working correctly, you shouldn't be able to leave the boat as it will trip within a few seconds of being powered up. Those are typically wired on the upstream side of the main AC cabin breakers so that they are powered all the time if the power to the boat is on at the shore power entrance on the boat.