Re: Gas vs. Diesel
Provided that you can get gasoline in your cruising area, and your insurance premium is not too loaded as a result, I would be more interested in the overall condition of the boat than whether the engine was gas or diesel.
Well maintained gas engines, with proper blowers to ventilate the engine compartment, are OK if you are meticulous about ignition-shielding and don't spill fuel or do silly things with power tools etc. Tens of thousands of power boats run gas and don't blow up.
A gas engine may only have half the life of a diesel, but that is still a lot of hours for most non-commercial users. Easy and cheap to overhaul when the time comes.
Or, at overhaul time, throw it out and re-engine with a diesel.