I have a small collection, I mainly buy them to get my hands on the artwork or a family member bought me the game and grabbed the guide for my convenience. Probably my three greatest gems are the original SNES guide for Chrono Trigger, an FFIII (VI) complete guide that actually has early translations of stuff taken from the Japanese World and Character Guide Books for FFVI. I also have the Xenogears Strategy Guide, which much like the Official FFVII guide, has a bunch of missing stuff that you would think a guide would have gotten.

I never use guides the first few times through a game, unless I truly get frustrated at something. The MegaTen games are the only exceptions mostly because Fusion can be really tricky and it's not fun killing an hour trying to get a fusion to have a certain ability only to read later that the fusion monster is incompatible with the skill. After a few playthroughs, I'll read up on it through a guide or gamefaqs to see what I've been missing or learn more about the underlying mechanics.