you are track
Don't listen to all the insurance talk above. The majority if not all states protect consumers from the type of behavior listed above. A company knowingly offering below "market value" on a actual cash value policy is looking for a class action lawsuit. I would though check to make sure the value they are offering is inline. Mistakes can be made.
If you take out the right policy (which you have) you don't need to worry about any "negotiations". Agreed Value policies are the only way to go whether you have Geico (Ski Safe), Progressive, etc.... Most companies do not even care what you tell them the value is as long as it is under $50k. Over $50k they would want a marine survey.
The fact that they are giving you the Agreed Value and letting you keep the boat is awesome. Take the money and boat and run. Don't fix it, its not worth it. They are likely letting you keep the boat because their cost to dispose less the likely salvage return is not cost effective. You however can part it out and make some nice money on top of your settlement.