When buying a House OR Boat fixing stuff that should already work may make it more desirable on the resale market but it is always questionable how much you will get back
The less you pay the more likely the systems are near the end of there useful life.
"Deferred Maintenance" is the painful bite that reality puts on bargain-obsessive boat shoppers.
You might find a 40 year old boat with all needed upgrades done, at a really low price because the owner just lost his/her job... but do not count on it happening often in the real world! (And being first in that line is a matter of luck, too!)
More likely you will find a classic Cal, Ericson. Tartan, or C&C that needs some major upgrades and maintenance. If you find one that has all the work done already and is priced twice what the others are, it's probably worth every dollar.
In the end, you have to live within your monetary
budget and your time
One place to look, other than the Classy Classifieds, is the "for sale" forums in owner sites like EricsonYachts.org: The Starting Point on Ericson Yachts!