This is great with one of those mini cucumbers sliced into matchsticks and thrown in. It's also relatively inauthentic, FYI, so you could try combining it with the Omnivore's Cookbook one, perhaps. Or just have it as a no-one-to-impress meal.
Broth tasted better before boiling it. Maybe serve it as is, or add the miso after boiling? Taste and experiment. Also, don't slice the mushrooms too thinly.