I'm not sure what property prices in Dublin were like in the 60's but, as Michael Noonan said he bought a house for 3000 punts in the early 70's, I imagine they were in that region. Some of the mortgage was already paid off, so the insurance would have covered the balance, which may have been a couple of thousand punts.
Apart from the principle of the issue, which you may feel needs to be pursued, the legal, technical and personal time costs of chasing this issue may not be worth it. I am pretty sure that even if you turn out to be right in your belief that the insurance didn't pay out, they would only be responsible for the exact amount insured, at the time.