There are commercial sock yarns where the traditionla wool/nylon blend is mixed with a bit alpaca. They are a bit more soft and nearly as long lasting as yarn without it. You can say that the 5% Alpaca in the yarn will take 5% off the life of the socks ;)
I have some Norwegian sock yarn with only Alpaca and Nylon. Very very soft but I think these socks are not meant to be worn in shoes, they are for keeping you warm and cosy at home, on your sofa or even in bed.