What does your surveyor advise?
A prepurchase survey shouldn't be just a check list, it should be a full narrative report that includes recommendations and even estimated costs to correct. You also be able to discuss any issues with your surveyor both during and after the survey, and ask his/her advice. A few small blisters on a 20 year old boat is no big deal...that's prob'ly all the blisters a boat that old will ever get. The high moisture reading may or may not be a big deal, depending on whether there's also any softness too. So talk to your surveyor...find out just how serious he/she thinks the moisture problem is and what kinds of problems it's likely cause later. That's what a survey is for.