This really doesn't have to be all that hard.
My experience buying houses, boats, etc. is to be nice but look out for your own interests.
If I'm up against an owner who doesn't want to come down on the price I'll counter with "I'm offering this because X". It's been surprising how often just giving a reason for the offer has broken the ice. If they still don't want to move on the price I move on. Life's too short and there are other boats out there.
Going back to that owner who's held that high price for a while can't hurt. They may have gotten to a point where they're finally ready to sell - and you might be the only taker because everyone else has written them off.
As for making money on boats - well somebody hit the lottery for $500 million - doesn't mean it's likely to happen to me. The money I spend on the boat is the same as money I'd spend on vacation, it gives me pleasure, end of story.
When it's time to sell if your boat is well maintained, clean, shiny, smells good and the lockers aren't filled with junk it will stand out from 90% of the boats on the market. That means it will likely sell faster and for a little more money than similar boats.
Hope your search is going well, you need to get on the water before the season's over