I don't pay full-price for them, but I will pick-up the codebooks when I see them cheap at Goodwill. Just more convenient than logging into your computer or your phone to look them up if you need one.
But I don't do strategy guides, for the most part. I don't like getting spoiled in a game. I want that sense of exploration and moments of surprise. I do make exceptions for massively-huge games like Oblivion or Morrowind because if not, I'd probably miss-out and a LOT of stuff I'd never discover on my own.