Are 3e books still useful for 4e campaigns?

[Filaristil]

Hi, I'm just wondering if books designed for 3rd edition are still useful for 4th edition campaigns. I've never played 3rd edition (And I'm not sure I want to), but some of the books sound like they could contain information helpful for a few campaigns I want to run. I know that a ton of people pick up GURPS books to use with other systems just for the information inside, but I'm wondering how useful the more mechanical stuff like templates would be for 4e campaigns. I know the rules aren't the exact same, but could I convert the templates to 4e using GURPS Update? I have GURPS Dragons, so would Update do for other 3e books what Dragons' 4e appendix does?

Sorry there are a lot of questions in one post, I'm just wondering if I need to learn 3e to use 3e books.

Also, just to clarify, I'm not talking about the more crunch-heavy books like Vehicles. I know those won't work at all. I'm thinking of specifically the creature-focused books like Faerie, Shapeshifters, and Blood Types; as well as the historical books like Middle Ages, China, Japan, Aztecs, Greece, etc.