I'm sure you've already noticed
this AP of The Bloodstone Idol on Story Games.
I'm not sure what your plans are viz-a-viz the list of questions for Spout Lore in the AG version versus the open sandbox of the Red Book version, but I think the dissatisfaction quoted below might have been removed if the list of questions had been available to spark player ideas.
I definitely could have been more flexible with the Idol. There's nothing in the book that says, "the character's can't do anything with it," it's just that there's nothing for it to really do in the context of the adventure. It's there as the subject of Grundloch's ambitions, serving the countdown clock of, "Does he wake it up and use it to wreck the countryside?" I should've been more flexible and made up stuff you could do with it.
Hm, what I could've done, when you were Spouting Lore and learning about the Idol, was detail whatever process was needed to go through to control the Idol--i.e., what Grundloch was doing. Then you could've decided whether to try and control it, etc. I didn't do that because it felt out of the scope of the adventure, and again, fictionally, it felt like you guys weren't powerful enough. Le sigh.
Personally, find the "tell them something interesting and useful" harder to run as a GM than a "How can I make it do _____"-type question too.