Sourcebooks and fluff

I have a strange love/hate relationship with sourcebooks. I like cool new ideas, whether those ideas are rules ideas or adventure ideas. However, I don't like fluff. What's fluff? It's different for everybody but for me it's setting information that doesn't directly affect play. For example, I don't really care about the history of a setting unless that history is repeating itself somehow.

I traded for a bunch of sourcebooks recently and got the following (mostly AD&D 2e but the Survival Guides are AD&D 1e):

The Castle Guide
The City of Ravens Bluff
The Complete Book of Elves
The Complete Fighter's Handbook
The Complete Priest's Handbook
The Complete Ranger's Handbook
The Complete Thief's Handbook
The Complete Wizard's Handbook
Demihuman Deities
Dragons of Triumph
Dungeoneer's Survival Guide
Faiths & Avatars
Monster Mythology
Powers & Pantheons
Tome of Magic
Wilderness Survival Guide
Wizards and Rogues of the Realms

I did some cursory skimming of The City of Raven's Bluff. It's almost entirely a setting book and there's a ton of history in there that doesn't look like it affects current adventure hooks at all. I'm hoping I'm wrong and there'll be tons of adventure hooks that jump out at me when I read it in detail but i have a lot of reading to do and I thought I could ask for your help here.

What is fluff to you? Have you read the books above? Are they full of fluff or full of cool ideas? What are some examples of sourcebooks that you have read that are the best at being full of cool ideas? What are some examples of those are full of fluff in your opinion? What are you looking for in a sourcebook?