I''m confused... I did a quick BUCnet price search, and it shows the price range of a ''85 Nassau 34 between $38k - $43k and the price range of a ''73 Irwin 32 between $16k - $19k. Now BUC does not know everything, but it represents the numbers that these boats have sold for recently. I would think that for your Irwin 32 at a low of $16k plus $35k cash, you should be able to get a boat worth about $51k. That puts you in the price range of a nice 34 Saber, a boat that is WAAAYYY better built and designed than the Nassau.
Did I miss something, or did you find the bilge lined with gold nuggets? It sounds to me like you have run into a crafty broker who is looking to make a killing at both ends of the deal. To get all the money for the Nassau he has on his lot, and then later, make a big profit on selling your boat.
Find out what: 1) what is he selling you the Nassau for. The actual number, not the net plus trade in. 2) What is he actually giving you in cash dollars for your boat, again not just some "net" figure. 3) Does he also offer "Convenient Financing" at his brokerage? How competitive are his rates compared to outside lenders? Captive finance programs usually have a substantial kickback to the broker. 4) Did your broker recommend the surveyor? 5) How long has this brokerage had the Nassau in their yard.
Finally, did you go into this deal looking for the Nassau specifically, after doing your due diligence and finding that the Nassau was the boat for you? Or is the Nassau something that the broker steered you towards after finding out a little about the budget and size you were looking for?
As Jeff mentioned, the deal seems a little too staked in someone elses favor. Not knowing the particular boat, this is all just conjecture on my part. But something feels like a foul wind here.