A boat 30 years old, which has spent most of its life in a marina, its sails rarely seeing the sun , rarely leaving the forepeak, or the garage, for months and sometimes years on end ,is not likely to have much wear, or UV damage on its sails . Her rigging and mast are not likely to have much metal fatigue, or corrosion. If the engine is not seized, its unlikely to have much wear and tear.Thus, age of a boat is no definitive indication of its state or real value. Such boats can be a real deal, as can boats who's owner is dead, or in an economic bind ,and the family just wants to get rid of it. Don't judge the value of anything by the price tag on it. "You only get what you pay for",is a sleazy used car salesmans line, which has sold a lot of lemons for grossly inflated prices, and caused people to ignore some great deals.
With a good ,sound, older hull as a good, solid base ,one can spend a lot of money and time, and still be ahead of buying a new boat, especially if buying new includes bank interest. It is an interest free, pay as you go arrangement, with lots of enjoyable cruising in between, and a lot learned, making you far more independent and able to deal with any problems later, by your own hands, at sea, or overseas. People who only solve problems with a cheque book, tend to be quite useless, when things break or go wrong in the middle of nowhere , far from any boat yard or mechanic.