Actually, there is some "salvage" value in old sailboats, the scrap lead or cast-iron in the keels. Any usable parts would be a gold-mine to anyone trying to restore a sistership, just need to connect buyer to seller. The various fittings (blocks, cleats, rails, shaft and prop, etc.) might pay for the cost of disposing of the carcass in some areas.
However, the unfortunate fact is that far too often a boat (power or sail) sits "abandoned" in someone's private yard or a boat yard, or on an isolated mooring.... until it is far too late to save the boat. The owner really has no interest in using the boat, but won't sell unless someone offers top $$ for the boat! Every time that I see one of these poor boats I dream of buying the boat for it's present value, then after cleaning her up and fixing things... selling for what the owner is asking.... Hey, it is a great dream... but won't ever happen. There is an old Columbia 7.5 (25' LOA) near my home that has sat in hte owner's yard under a lot of trees for close to 10 years. He did list her on Craigs-List for a while, but no takers... he then listed her again for FREE, still no takers! On the outside, she looks like a day or so spent with a powerwasher, then a dat or so with a power buffer and some rubbing compound would bring her back. However, the inside has got to be a disaster, since hte compainionway has been open (although hatch closed?) for many years!
Many of these boats would find new homes if the owners were willing to "cut their losses" and sell for a price based on present condition, or if they were put up for sale soon after their last use. But, too often the boat comes out of the water and then sits (often without proper covering or winterization) for far too long. Then the owner tries to sell but prices the boat based on what they paid for her when in great condition. The boat has lost value due to neglect, but the seller stil lwants top dollar and so the boat continues to sit. Sometimes the problem isn't neglect, but that the owner is ready to sell, but can't find a buyer interested in a classic, too many new buyers only want the latest design, a "condo" on the water with all the latest goodies! The type of boat many of us would never set foot on even if we could afford the new boat price. So, their old boat sits....... rapidly losing value, but not always losing potential value. Unfortunately, the market for good old boats isn't increasing, since many of us that would seek out these boats are aging beyond the desire for a boat. Old fiberglass boats don't rot away like old wood boats, they eventually do reach the point of being beyond help, but by then they are borderline "hazardous waste" and difficult to get rid of. There is some research into ways to recycle fiberglass, but it hasn't progressed to a point of providing much hope for a solution yet.