The previous survey can be handy especially if it identified issues. If so, ask what was done to resolve those issues or if they still exist. Look at the previous survey for signs that the 'accredited' surveyor was on the ball. One item I look for is that the moisture report includes the weather conditions, when the boat was hauled and the make and model of the moisture meter. If the report does not include such info, I have my doubts about the quality of the report.
All that said, this is what I always tell folks who ask your question; If you don't get a survey and the boat turns out to be a really bad choice due to unforeseen conditions, would you be seriously hurt financially and/or loose sleep over your decision or would you look at it as just a bad decision and a learning experience?? If it would hurt, I advise both a hull survey and a motor evaluation.
By the way, the difference between an accredited surveyor and a really good accredited survey is one who has first hand experience with your make and model of boat. You should ask a potential surveyor what he or she sees in the field and what he or she would specifically look for on your model.
Surveyors who do insurance claim investigations often have a broader knowledge base.