I think it all depends on whether you look at it from the seller's or the buyer's perspective.
As a seller, you are shooting yourself in the nuts if you don't present a neat, clean, well sorted boat. Anything else is a turn off, and as this thread demonstrates, causes most buyers to reject the boat without looking any further. I would guess that a poorly presented boat will cause the seller to lose 50-75% of their available market of buyers. That's as bad as saying that any interested parties who's names begin with A-R should just go away. Pretty darn stupid of a seller, if you ask me.
As a buyer, boats that are poorly presents can be real opportunities. The seller is probably frustrated with the lack of interest, and likely to accept a very low offer. And as was pointed out, you are probably going to scrub the boat head to toe, replace all the soft goods, and update AV and nav electronics anyway. So if you are part of the 25% who can look beyond the surface, you might find a real diamond covered in a layer of dirt. What you really know is that you are buying from a fool, and that is in your favor. Now you just need to assess the boat.
The same is true with cars, houses, etc.