I just bought a 79 Pearson 10M. The boat is in great shape and was well maintained and cared for. The surveyor absolutely loved the boat and said he has done a lot of boats and said a lot of even newer boats looked worse. He said he had done boats even a few years old that were in very bad shape, so age isn't the only factor.
The bottom line is that if you find a good boat from a brand that is known for solid boat construction in those years and the boat is well maintained, there should be no reason to be concerned. Get a good surveyor that knows the type of boats that you are interested in move forward with them.
All boats need some work, nothing in that vintage year is going to be perfect, so as long as you know that and the price reflects the condition, I say trust your survey and proceed from there.