The manned missions added tremendous additional scientific value, especially for the time period. They didn't have rovers with the ability to determine which rocks would be of value. The humans were trained to do just that.
Plus that wasn't the (only) goal of the missions: beating the USSR there was a stronger motivator.
'We feel the need to beat the USSR' wasn't mentioned in the letter to the nun - perhaps because being able to boast about winning a race might appear to be less important than people suffering in Africa.
Let me ask you this: Given the scientific advances made due to the first moon landing, do you think that the second, third, fourth, fifth and sixth moon landings also added tremendous scientific value? Do you think there should have been a seventh?
No, because we clearly weren't willing to commit the resources to make our efforts pay off in the long run. Who knows what might be possible now, if we had used the money we spent on the Viet Nam war to successfully establish a permanent manned lunar colony?
The sixth, certainly; it was the first that had become routine enough to send a professional geologist along. I'd go so far as to say that most of the scientific value in 12-16 was in making 17 possible. There absolutely should have been a seventh, eighth and probably ninth; scientific targets had already been picked for the next three IIRC.
After that, maybe not so much. But the program was designed with ~nine landings in mind, and that's what we should have done.
Plus that wasn't the (only) goal of the missions: beating the USSR there was a stronger motivator.