When dishes are missing something, I often try a little sprinkle of either ancho chili powder to add warmth and umami without any real heat, or MSG for straight umami (or both). These don't always work, but do work surprisingly often.

Here you can get MSG as a small canister product called Accent in the spice section, though I've also seen giant bags of generic MSG at the Asian grocery. It just makes things taste more like themselves, and a tiny bit goes a long way. I keep a reused spice jar with a mix of salt, black pepper, and Accent in my 'right next to stove for frequent use' stash (which also contains garlic powder, onion powder, salt, and pepper). That mix is great on chicken before roasting, too.