Originally Posted by CharlieD
+1 and that plus is really big.
Also seconding the salt part.
You don't need to make it super salty, but when the salty receptors on your tongue are agitated it will actually cause certain aromas to become greatly enhanced (and aroma is where the real magic happens with taste).
Although theoretically depending on the oxo cubes they should have a decent amount of salt in them already.
Also adding something mildly acidic to the mix will draw out some of the vegetable fats into the broth
While animal fats are right there and in your face and can be rendered fully without adding a solvent, a lot of vegetable fats tend to require some chemical coaxing, and something acidic like a vinegar, or citrus flavour (depending on the overall profile you are going for) will help with some of that coaxing.
And if you want to neutralize the acidity after it does it's work just add something bitter to the mix toward the end.
Hope this helps!