Please tell me if I'm being hideously deluded and naive.
You are being hideously deluded and naive.
Just like the rest of us
I bought my slightly run down boat for $15K. After about $40K in a new engine, sails, rigging, electronics, misc. fittings and ground tackle, interior joinery and exterior refinishing, ( I did almost all the work myself so very little labor $ included) the market value of my boat is...
...$15K (Using it to live aboard and cruise for the past 22 years: Priceless)
I have known people who manage to make a few bucks buying (Or acquiring for free) run down, neglected boats and refurbishing them to just seaworthy condition for resale. Most boat owners, however, will tell you that any project will cost triple what you plan to spend and nothing you add to an already seaworthy boat will increase resale value enough to generate a profit.
I have a well known bias for small boats and an aversion to giving advice so I won't recommend any particular boat. Do your own homework and you may come to the same conclusions I have.
If I were starting over, I would spend a lot of time hanging around boatyards and harbors networking, eyeballing and learning to tell the difference between structural and purely cosmetic deterioration. With a $75K budget, I would look for a stout, older (1975 or earlier), fiberglass boat that could be had for $25K or less. I would look for it to have good ground tackle, winches and a good inventory of sails; Expensive stuff if you have to buy it new. OTOH, basic electronics, VHF, depth sounder and GPS are relatively cheap.
Sailboats with bad engines are common and cheap. Learn to deal with the internal combustion Rumble Monster yourself and save a bundle.
Rigging, for some reason, flusters most boat owners. Educate yourself (Read Brion Toss). Rigging is simple: Measure, mark, cut and fasten. I would replace standing and running rigging on almost any used sailboat and this can be VERY expensive unless you DIY.
I know this sounds like advice, but really, it is just my opinion and I am certain there are others who will disagree.