Valiente offered some very solid advice. I would call particular attention to this point:
"3) A very important aspect is care and maintenance. A single owner with some skill might have bought Typical 30 foot Cruiser in 1975 at 40 and has had it put on the hard...properly...every winter since (In the North East, you have to think that every boat is only X years old times 7/12ths. Against this lighter use are the structural strains imposed by craning and cradling and the potential for leaky cores freezing and thawing every year, destroying the bonds). Anyway, said skipper is 72 now and is maybe looking to pass the boat on to a responsible buyer. That's the sort of deal you should look for. Well-cared for boats have frequently been repowered once and electrically upgraded twice or even three times in 32 years."
By way of illustration, one of my brothers is hoping to upsize from his Tartan 27 to accommodate his growing family. We recently went together to look at a "'70s Era Boat". This particular make and model is known as a rugged design with the potential for serious longevity. We were hopeful. Upon examination, we discovered that this boat must be one of the few from that vintage that has had ABSOLUTELY no upgrades made to it. Everythng (engine, sails, rigging, electrical, electronics, cushions, upholstery, etc etc) original, and completely worn out. It was like a time capsule -- the bad kind.
You do not want a boat like that. Find one with the upgrades that Valiente described -- the kind of upgrades that diligent owners would make over the yearts to a good old boat. That doesn't mean there won't be any projects, only that you shouldn't have to inherit ALL of them.