The way I see it is, there's no benefit to you if your involvement with a guru is to follow, support, admire, and believe. If that's all you do, then the benefit only goes to the guru. On the other hand, if you believe that any benefit will come through building your own understanding through work, thought, and experience, and they influence you to do this work, then you will benefit, and it hardly matters if they personally have any great insights or not.
There are gurus who encourage the first kind of involvement at the expense of their students, but different people can take different things from the same teacher. Some people are strongly predisposed towards one or the other forms of involvement. Some people want to just sit and listen, and they'll get little benefit whether they're listening to a saint or a fraud.
As for intellect, when someone is presented to you as a guru, all or nearly all of their specific insights are going to be well-worn, recycled cliches. A guru is more of a coach than an intellectual. An intellectual's job is to say new things, or old things in new ways. A coach's job is to say what you need to hear even if it's been said a hundred million times before.
For some reason we get this all mixed up when it comes to "spirituality," and we believe everything hinges on the quality of the ideas. Instead, imagine your kid's soccer team is being coached by the great soccer manager Carlo Ancelotti. Imagine that they spend every practice sitting on the ground and listening to him lecture them on technique and tactics (not that he would make this mistake.) Meanwhile, the other teams are coached by parents who know nothing about soccer, who run their teams through dribbling and passing drills they looked up on the internet, followed by some chaotic scrimmaging. Your kid's team is not going to win a single game, even though they have a "true intellect" for a coach, and the other teams are coached by frauds.