Regarding a boat's value and how what you do to it affects it's value.......
I don't think you can ever add value in terms of monetary value with a boat unless its a collector boat like a Hacker Craft or Gar Wood runabout of the like. People say, "I sold my boat for more than I paid for it," but in most cases that's numbers of dollars, not dollar value. Our boat sold new in 1973 for less than half what we paid for it in 1998. But if you calculate the difference in dollars adjusted for inflation and other factors, our boat lost a fair amount of it's actual value during that 25 years. At the time we bought our GB36, new ones were selling for a bit over $300k equipped to be usable. That is almost ten times what they sold for new in 1973.
So with relatively few exceptions, a recreational boat almost always loses value over time no matter what you do to it.
The other factor affecting value is the selling price envelope for a given make, model, and year. We are considering having our old GB36 completely redone. New engines, generator, hull and superstruture totally reworked, new interior components throughout, etc. The cost of doing this will far exceed the current total dollar value of the boat. But if we do it, we won't be able to sell our boat (if we wanted to) for any more than the top end of the price envelope for 1973 GB36s.
So the "added value" of having the boat totally reworked will not be in dollars because we'll never see them back, but in what the boat is to us, how the overhaul enhances the value of the experience we get from using the boat.
You are 100% correct in that statement. You will never see the full value of a refit if you sell the boat. The value of a refit comes from using the boat, with the confidence that all is "right" with the boat, and that you are going to have less to deal with for a certain period of time.
Our 2001 4788 is a prime example. The average market price for this boat is around $225K. With great examples being upwards from that and poor examples lower. The "envelope" for this model right now is in my estimate between say $170 and $260K
We bought our boat for $130K as a "project boat" The boat suffered from defered maintenance. The engines had high blowby, the generator had issues, the list goes on and on. Typical laundry list of a boat that had been purchased new and just driven.
We repowered the boat with reman engines, put a new generator in, caught up with 100% of the defered maintenance, and basically brought the boat up to 100% new condition. As part of this, we added several systems to ther boat including waste treatment, heat, satellite communications, watermaker, etc... A long list of new "stuff"
I did none of the work on this project. I have the most of the skills but I recognized up front that I do not have the time. We hired a first class large shipyard to do the work.
Our total refit cost was something over $150K. Since I bought some of the parts myself I don't have the full numbers right here. I think I spent another $20K or so on parts I had shipped to the shipyard for installation.
So, now I'm into the boat for $280-300K+. I would never get that out of the boat if I sold it today.
But....
I'll keep the boat and get the benefit of owning a basically new boat. One of the best benefits is a lack of suprises. I'm not going to walk up to my boat in the near future and have Mr. Big Bill waiting for me to pay up. I can drive the boat, and keep up with maintenance, I do not have to catch up.