This thread is in two parts, one the obvious appreciating of a well made albeit older vessel and two, the desire to seriously upgrade the same vessel with money not necessarily the driving force. Let's be honest, if money were the holy grail none of us would have the vessels we do.
As retirement approached we set aside "play boat" money to do on the water what we are doing. We assumed we would get little of it back and moved on. The money we are pi$$ing away on the boat and journeys is buying lots of pleasure and emotional reward. Our financial threshold for this endeavor is less than some and more than others can and do choose to spend.
To some, money is to be carefully husbanded and to be spent only on OUR relevant things so it can be left to family, charities and the tax collectors. But what is relevant to one may not be to another. If one has the free capital to sink into a boat and the opportunity to take what is to many a very iconic vessel and bring it to the next level, why not do it? The JD 4045 or fully warrantied Cummins reman mechanical will be a marvelous addition. Don't forget to ballast for the weight loss.
There are many boat shoppers, me for one, that would relish the chance to purchase a good solid sea boat that has been seriously updated and not cored, not steel, not wood, solid bones, the ability to get me safely back to port and emotional joy.
For some, the love affair with a 2 stroke DD is never ending. Having been in the middle the commercial diesel world for almost half a century and watched non DDs perform on a tightly watched opex and reliability basis I am thrilled they are gone and have been for many decades to be quite honest.
So to the OP, bringing this great vessel up to the 21st century is a unique chance and opportunity. If you have the throw away money enjoy the journey the same as art lovers, rare book collectors, equestrians and house remodelers do. It will be every bit as good as a similar sized newer Selene, KK or Binatow. Don't get caught up on resale, enjoy the redo and let the future pleasure you will gain be yours to savor.
Last but not least, pick a refit yard wisely.