"Moreover she only cruised in the local area where diesel quality is high but I would maybe be a bit nervous to refuel somewhere I am not sure about the fuel quality."
Sounds like you would like to travel further with no issues or concerns about fuel by making a few modifications now within a reasonable budget.
That is a great thought and very similar to where I was and what I did in the past with a couple of boats. IMHO - I would suggest a few fairly cheap methods to get there....
- Add a bulk spin on filter between the tank and you existing filter that will take up to 90% of the load off of that filter.
- Add an incline vacuum gage for the bulk filter
- Add an inline vacuum gage for your existing filter.
If you do your own work all the above should be less than maybe $300 and the additional filter will bring your filter changes down by over 400% or more. This would be a good time to also renew any hoses or fitting in the fuel system that may be potentially annoying you. Here is the link to Tony's fuel filtration article....
Fuel Systems & Filtration - Seaboard Marine