These are not cut and dry questions. I watch the used boat market quite closely as I am often called upon to help people find their dream boats. While some boats seem to be holding pretty level values or going up in value, others have dropped quite precipitously. While there are some trends they are not absolute and they really can''t be counted on.
The general rule is that non-competive race boats with minimal interiors have lost a lot of resale and can be bought cheaply. That would be true of boats like the Olsen 30, Old One-Tonners, Farr 37''s, J-36''s, J-27''s that sort of thing. Old race boats with decent interiors have gone up in value. So boats like the S-2 9.1, Laser 28''s, Express 37''s and J-35''s with the operable ports and cruisier interior package have actually hit a low and seem to be coming up in value.
1980''s middle of the road coastal cruising boats like Pearsons, Odays, Tartans, Sabres, C&C''s seemed to have held their value pretty well but their prices seem to be separating. As they reach 20 years of age they are taking more to keep them up. Standing and running rigging
, electronics, deck hardware, sails, engines, interiors, and the like are in need of major repairs
or replacement. Owners who have done these major overhauls are asking very high prices (the brokers tell me that they are not actually getting them but they are getting higher prices than anyone would have expected a few years back.) The boats without this kind of upgrades are plumeting in value as these cost of doing this work far exceeds the value of the boat sometimes. Still people see the higher asking prices and think that these boats have actually gone up in sales price for all of that model.
Similarly, 15-20 year old so-called blue water boats seemed to be holding their value for a while but I noticed that similarly the earlier models seemed to plummeted. There is noting more expensive to put together than an old blue water boat because all of its parts are so heavy duty and expensive. Where models have had minimal changes, refurbished boats can demand pretty high prices because compared to new boats they are still cheap. BUT older unrefurbished blue-water boats can be bought quite cheaply and then som poor S.O.B. has to try to put these things back together.
Boats by the Big Three seem to plummet quite quickly after they are new. Typically they sell for thier "base price" which ignores the additional 10% to 15% that covers all of the options, add, ons and spares that get added to the base price. Oddly enough, Good clean versions of these common boats can still demand 50% more than the more clapped out versions and boats like the Beneteau First series can often sell for their purchace price 12 years later.
So like I say, there are not hard and fast rules.