Provided that you're willing to shed a good forty or fifty smackeroonies for it, I highly recommend it. It's hard to comprehend just how indispensable that guide must've been before the days of GameFAQs for divulging secrets one could never figure out otherwise, such as the unspecified timings for every special attack or the purpose of the B'Tub Ring.
I forgot they had the timings for each special attack. I just used it as a "do what we tell you to get the hundred percent" guide rather than playing on my own, due to an unfounded fear that the game would be difficult if I missed all the secrets. In retrospect Super Mario RPG is incredibly easy (the 30-level cap helps). But it's just really cool to snag that Ghost Medal you know.
What I ended up using the guide most for was to glance at all the enemy statistics in the back. Now I know there were countless errors in it, but I liked glancing at the numbers to gauge roughly how difficult an enemy would be or to find out what they were weak against. I didn't think Jinx would be a problem... well, the stats say otherwise.
But yes, the purpose of the B'Tub Ring... would never have figured it out on my own. It's great that it leads to an awesome item that saved my hide in Nimbus Castle when I was down to no health and no magic. But I never got the Attack Scarf or Super Suit (I wish it was Super Jacket like the guide said), I wasn't that good with timing.
I think if I didn't have player's guides, I would have learned that any unlikely sure-to-lead-to-death thing I could do would probably lead to a bonus room. So I would have died a lot more in games than I do now, trying every possible combination. The reason I use guides to "help" me through the first playthrough of any game is that I don't feel like playing through the game a second time to get all the secrets. Too much time for my short attention span. I gotta have it all, and I gotta have it now. Except when something's so insanely difficult that I accept I don't really need it, like that one Shine in Super Mario Sunshine where you're in a pachinko machine.
I remember the thing that stumped me most in Super Mario RPG was figuring out the password to the Sunken Ship. I didn't even think it'd be a real word because I couldn't find any real words to form out of the letters, so I thought "maybe the password is a jumble of letters". The password seems obvious now, but I honestly didn't know what sat at the bottom of the sea other than the Titanic. That was the one and only time I called the Nintendo Hotline. And the guy just straight up gave me the answer, as if "okay, you give up, here's what it is. Tell your friends so I don't keep getting the same darn question". I seriously want to know how many questions to that hotline were about the Sunken Ship password, I was under the impression that that puzzle was hard.
I also used the guide to tell me which of two boss characters to go after during boss encounters where you had to fight two guys. That boss fight at the end of Booster Tower (after you successfully get through the fun "where's the Mario doll" game) is a killer.
Also, there's some 3D models in the guide that you just don't see online. You can't find a 3D model of the enemy Bahamutt anywhere. There seems to be a lot of Nintendo promo art that just gets lost to time. That's some cool art, man, like the Banjo-Kazooie art of the duo in a swamp when Nintendo was covering the upcoming E3. Why doesn't the internet keep that stuff around?