It is quieter, more private, and always better ventilated. But, if you like marinas, and want to spend periods tied up, you need to add in a factor for this. Food for onboard consumption does not seem to be a huge item compared to others, and our experience is, for the most part, that the food budget runs about the same as on land. The big variable in both of these is where, what, and how. There are exceptions in oil-exporting countries.
Insurance varies with the market conditions, age and type of boat.
Flights home - now there is a huge variable. Easily as costly as the rest put together, which we've been finding out personally in the past year. No way to give you a ballpark here, except to say, if you find a really good deal, on an airline you trust, grab it. This was on a Friday. Another variable is maintenance.