In comments and answer to this question, the time it takes to train for an Apollo mission is mentioned several times as a factor on the big rotation of crews. I figure that would actually play in favour of reusing crews, as most of that year of training would presumably be redundant.
I can only picture the amused looks if a white coat came to Armstrong and Aldring in sept 1969 and told them: Ok, today we're going to learn how to land on the Moon.
On the other hand, some of the training might be mission specific (scientific instruments, driving the buggy, ... )
So now I'm also curious to know to what extent a full crew would need to retrain if they where to be sent back to the Moon.