Calculate yacht ownership costs?

Maybe. But replacing an aged system that still works is also preventative maintenance covering the burden of deferred maintenance costs. Now if you go from a Whirlpool to a Subzero, then the cost delta of new versus new is undoubtedly an upgrade.

Either way, it's still "ownership costs."

A Major Refit would be too.

Will it ad value to the boat beyond repair; Upgrade.
Will it fix defective options; Repair.

Sadly, repairing that dead 10 year old radar display no longer serviceable (less e-bay), is not an upgrade IMO.
Paint job refinishing to original, repair.

Replacing that dead water pump with an exact replacement; repair. Replacing that dead water pump with a better replacement pump because the original was not available, still a repair.
Replacing the ships water pump that notably improves potable water service may be an upgrade.

There is no easy answer.
It all has to come out of your check book.

Another thought; Some money is used to help keep a level of value of the boat, some money helps to improve the value of the boat.
When you re-market the boat in a couple of years, Normal repairs and maintenance will help keep lots of value after depredation.
Upgrades will ad value. Beyond your original decor & furnishings, improved A/C systems, Cockpit extensions, That baby grand piano with wet bar.

After my typing all this, it is still a fat grey line that may never be realized in black or red columns exactly.

There is also the consideration for how you like or dislike projects and improvements. For me, I really enjoy the projects and improving my boat. I do every bit of preventative maintenance and then some. Additionally, every year we do improvement projects. Some improvement projects are for function or visual and some just because I want it to be better. For example, this winter we are fabricating hot and cold potable water distribution manifolds to improve the plumbing system. Not because there are any leaks or problems. We are doing this to improve the system, add isolation valve capability, and make the plumbing more accessible. I would opine that most owners wouldn’t do these type of things. So my point is, you can spend the minimum just to keep things functioning or you can spend many times more.

That all makes sense to me but it made me wonder about the upgrade adding value. In what way? Resale price? I have found in my experience around small boats, say less that 65 feet, upgrades do very little to sale price. Boats seem to sell on the brokerage market with close attention to Comparibles. The things really compared are Manufacturer, LOA, Model, Year, Power plant, Layout, Overall Condidtion. But going from analog to digital radar (which is an upgrade) is hardly going to add the the selling price of two comparable boats.

Is this not true in the Yacht market?

You will never imagine how many times I deleted/edited/erased/re-typed/pondered; what I did post expecting this question to come up.
Hopefully when you ad that baby grand with wet bar, charter or future use was considered. It will be a vertical niche but it is an upgrade.
The receiving market will respond or not, to a taller selling price.
Just listing a X year, model X, does not quiet make it in the more personalized larger vessels (IMO). It will be the listing agent to help sell these mods (upgrades) and hence, why the larger vessel brokerage firms are more aggressive/competitive/visible/specialized in selling these larger platforms.

Now, selling a 2010 SeaRay, it is by book value. No room for a piano or better bar or any real up grades.

I would like the listing broker to make the upgrades shine on any size boat, as you said a 2010 SeaRay is a 2010 SeaRay. Thanks, that is what I was thinking.

Hows the boat shopping going?