I will start with my two homes. The first home my wife and I bought, the second home we inherited. The first home was so bad my mother refused to come into it. We owned it for 12 years and with the increased equity, took out a large loan and rebuilt it from the studs up, and a second floor was added and a new addition on one side of the house also installed. A 900 square foot home became 2,600.
This house was in a well off area in North Vancouver which meant we did okay when we sold it in 2016. Before moving in to the inherited house, I bought an older Winnebago motorhome where my wife and I lived for eight months while that house was taken back to studs, some rooms modified, new everything including plumbing and electrical, heat pump added, hooked up to natural gas and gas appliances added with a tankless hot water system.
Same thing with a bike I bought. I wanted a three thousand dollar bike but I didn't want to pay that much so I bought an older Specialized Tarmac Comp (carbon fiber frame), added new tires and wheels from Italy, new Shimano Dura Ace compact in the front, new shifters, etc.
In other words, these old things were brought back to life, I got more for less and because of re-designs and re-equipping, they became "my and my wife's" home, the bike became "my" bike.
I've done the same with the boat I purchased which is at least 50 years old this year (might even be 55 years old) but the basic bones of the boat, so to speak, were solid. I have had the boat completely gutted. Amazingly the hull is original build fiberglass over wood and other than one small spot on the transom, found after the engine and leg were removed, the entire boat hull and top side, also wood, is free of mold and rot.
If you are going this route, you are probably better off with a single engine with bow and maybe stern thruster, than two engines. So others are warning you about plumbing, fuel and water tanks, etc. But who cares, I have removed those and replaced with new equipment. Some new storage as been added, a smaller Norco dedicated freezer added, new stove/oven, new head, new cushions, new deck covering inside and out, new electronics, new rib and 9.9 Yamaha, new davits, raised and widen'd swim platform. Even the dinette table has been replaced with what I specified as an "eye candy" table. Efoy and new Firefly batteries for my house bank and new bow thruster. The engine although about 60 pounds heavier but the leg significantly lighter, the horse power has been increased by 50 % (express cruiser with semi-displacement hull), the fuel tanks have been increased by 60% (but the old head holding tank removed and a composting toilet installed thus allowing the new gas tanks to take up that weight.
If you have the cash or line of credit, and lets say your budget is $250,000 you might be better served with a $40,000 and $210,000 refit. In my case, I can honestly say every square inch on my boat has been gone over in one fashion or another. I know that everything is new, does what I want it to do and will last for a decent amount of time. If you go this route, rebuild or replace the engine (why a single engine boat is better = cheaper to rebuild or replace). Some, including my refitter, told me not to replace the engine and leg, but after everything was dismantled it was clear replacement was the way to go. If you have work done on the engine or replace it, there is a piece of mind knowing it shouldn't be an issue for a long time. This piece of mind is invaluable in marginal conditions on the water. And don't be afraid to go older as long as the bones of the boat are decent. Heck a 20 year old boat is almost new... lol!