I'd agree with that. I've had my boat for 10 years, use it 70 days a year. My most
optimistic models say I've roughly broken even relative to using the charter boats, and
that's with two of us diving most of the time.
The best part of your own boat is that goes where you want to go, when you want to
go there, with who you want to go with.
We use our boat a lot but can't tell for sure how many days a year, I doubt we brake even relative to using charter boats, it is also 2 divers in my case, but regardless of the price difference, it is worth each and every penny.
If nothing else I would have to add to the charter boat's money, the cost of therapy or maybe even court costs and lawyers to get me out of jail after dealing with some of the opeators in this part of Florida.
Like you said: the boat leaves when you are ready to go, no one to wait for, and only the people you want aboard. It is trully priceless.
Even taking into account the after dive maitenance is worth it. My husband and I have been fine tunning the way we do things in order to streamline the maintenance. At this point we dedicate one afternoon a month for a good all around cleaning, the rest of the days is mostly a fresh water shower that takes very little time and effort, much less than what it takes to clean the fish we may get.
The only way I would be against having your own boat is if you never had one, and you have more than half a dozen charters than you trully like, available year round in your area.
I did while I was in South Florida, had a sit on top kayak for days when I was sick of people and for the rest I made a point of not going with the same boat too many weekends in a row. But then up here in the Florida Tundra the choices went down to about zero, don't know how locals do it without a boat, not planing to find out either.