Interesting information. I will check what the controller on our 54 supplies to the pump. It seems odd to supply a higher voltage to the pump that for which it has been designed. This again makes me believe the pump is actually a 24 volt model or else it would not last very long on 18 volts.
Fact is that the spare pump (ours still works) is very quiet and does not get hot. So whatever Italian magic is going on in this system it's not all bad.
I'm not so sure about the fresh water circulation. That will force you to keep a generous level of water in the tank or else the temperature will rise significantly. Polyester makes not a good heat-exchanger after all. Given the fact our watermaker is shot (and will take some time to be repaired), I see practical problems here.
My preference would be to have centrifugal pumps instead of the ones currently installed. Centrifugal pumps are much better in handling raw water (no valves).
So when are you to return to Curacao? Our 54 is actually less then 50 yards away from yours, on the same pontoon. Our hull number is 121 so I guess our boats were build more or less simultaneously.
We will go on the dry next week if all goes as planned.