I guess the issue is basically that you have an unknown vs a known. The Islander 34 is something of an unknown. I haven't been able to find much of any information about them. I don't think there were many made and googling just doesn't come up with much. Same thing for the Isuzu Pisces engine. The Pearson 303 and Yanmar on the other hand have tons of information available. There is an easily researched track record. The small areas of moist deck around fitting is a well documented issue with Pearsons from that time frame. To me its something that enters into the negotiation and should bring that price down to an equtiable level. Same thing with the leaky Racor. Both are fixable issues.
I'm curious what the general opinion is on the "unknown" vs the "known".