A Yachtworld search won't tell you the real value, because asking isn't getting. A broker would have access to recent sales and could probably give you a better idea of what a boat is worth.
Even the selling price data on the "soldboats" site is only as accurate as the honesty of the broker making the entry.
Better than trying to go only by asking price, tho.
Main determiner, as others point out, is CONDITION. Once a boat gets beyond about 15 or 20 years old, the value can vary by up 400% from the low end fixer-upper to the (rare!) turn key model.
The number of older boats with deferred maintenance costs that total more than the asking price is amazing...........
So take care of your boat and get your "value" out of it in sailing and cruising time. It's the only sure dividend you're likely to ever see.