The market value is the maximum price someone is willing to pay for your boat, and you should be able to get a sense for this by shopping around for a similar used boat in similar condition. I've sold a few houses and the first thing I do is go house shopping to get a sense for what my place is worth - it's the same with boats.
Then there's the value, which can be different than the price. The major components of a boat depreciate at different rates and if you can do some research to determine roughly what each component would cost new today and then estimate the service life of each component you can get a pretty good sense for it's value. For example, unless it's been damaged somehow I think an EagleCraft hull should be worth close to the cost of a new bare hull and you can get a sense for that by talking to a builder. The cost of aluminum is ~25% higher today (in constant $) than it was 20 years ago and it's likely that a new hull would cost the same as your entire boat did 20 years ago. Another example would be if your outboard has 500 hours on it and it's service life is expected to be ~1000 hours, then it's value would be around half the cost of a new installed outboard and Yamaha posts it's prices on line and you can talk to a dealer and get a sense for the installed cost. And so on.
Some people won't settle for less than a brand new boat - but sometimes there's more value in buying used and the more you know about the cost of the individual components the better you'll be at finding that value.
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