I may not be the best person to answer this particular question. I've yet to experience an idea that couldn't be made into an interesting story. (Maybe that's an indication of my own inexperience.) But I'm also a firm believer that anything can become a story if you're willing to put in the work.
However, a lot of this answer boils down to what your goals are. If you're wanting to write a book to get it traditionally published, there are some qualifications that a manuscript needs to meet. If you're wanting to write a book just because you love writing, all you need is your idea and the desire to write about it.
So, let's break it down.
The world of publishing is vast and yet quite intimate. I think from the outside it appears more intimidating than it actually is. As a basic overview, you have publishing houses--big and small, literary agents who represent: age categories (adult, young adult, middle grade, and children's--broken into chapter books, board books, and picture books), and genres and sub-genres (non-fiction, upmarket, book club, literary, genre fiction and then fantasy, romance, contemporary, etc.).
If the goal is publishing, you'll need to decide where it fits in the market. That means knowing your age range and genres. Every genre has an average word count, common tropes, and familiar themes. This is going to be one way you gauge whether your idea is "good enough."
As an example, I typically write young adult fantasies. The average word count is 75,000 to 90,000. My first manuscript closed at 93,000 words, and I knew when I started querying I might lose opportunities with certain agents and publishers because my word count was too high.
YA fantasy typically focuses on some kind of coming-of-age story. It may not be the main theme, but you can bet there's going to be an element of finding yourself tucked somewhere in those pages.
When I started writing that manuscript, my goal was just to write a book and see if I liked it. At the time, I wasn't really concerned with word count or themes. But when I finished it, and I knew I wanted to continue writing and pursuing publishing, I focused more on tailoring the story toward the market.
All that's great, but what about when you're just starting out? Well, I would say the most important thing is to read widely but also to read within the genre you want to write in. If you're not familiar with the market, you won't know if your idea can be made into something publishers and readers will want to see.
Regardless if you're publishing or not, you probably want to have an idea of where your story is going--even if you don't outline. You want to have an idea of the progression of the main character: what they want, what they're willing to do to get it, and where they will end up. What is the change they have to make? You'll want to know the villain, the secondary character(s), and what their goals are.
If you can build out all those concepts, then you probably have a solid story idea. And that's not to say you need to have every detail planned out before you write a word (personally, I like to outline but also leave my story room to grow on its own), but these notes can be helpful if you're just beginning and you're not sure where to start.
When I tried to write books back in high school, I never got past the first couple of chapters. This was often because I knew where I wanted to start but nothing else. Once I'd written what was floating in my head, I hit a wall. It didn't mean my ideas were bad, simply that I hadn't put enough work into making them a full-fledged story.
I heard V.E. Schwab say once that she knew a story idea was worth pursuing if she couldn't stop thinking about it. If she put it on the back burner and it kept pushing its way to the front.
Really, I think that's the most important thing: if you feel like you have an idea that needs to be put on a page, and you'll be able to steam all the way through, then your idea is definitely good enough. It might need some refining, but all stories do.
Write what you're passionate about.
Erin