That may not be true for all boaters.
It depends on how often you sail and how much fuel you use per trip. In addition, if you want to boat to a distant port, you need to be able to estimate if you can make it SAFELY on a tank.
If you burn 100 gallons in a typical week of boating and you boat let's say 25 times a year, that would cost about $12,000 a year based on current gas prices at fuel docks. Getting 10% better mileage will save you enough in a year to buy about 37 fuel filters