First, I have to point something out. Bradygames published the guides for the original releases... they did NOT publish a guide for the Remix of Kingdom Hearts 1.5. Prima did that. Prima are the guys who would probably publish a 2.5 Remix guide.
Second, while some say, "Use the previous official guides," just remember that the Remix stuff includes new content that those guides won't cover.
Lastly, getting a strategy guide isn't actually always about using it. Those who got the 1.5 Remix Guide will note it was a collector's item. Yes, you COULD use it, but most strategy guides are published and released now to complement the game they're released for not necessarily just to be a tool for the game. In other words, it's perfectly okay to have it just because.