Im a vegetarian.
I do make my own vegetable broth ( sometimes) with scraps .
Basically any vegetables with water, salt ( sometimes herbs ) then strain.
Will definitely add more flavor.
That being said, certain veggies will give more flavor and will change the end result of the recipe that you use it in. For example, mushrooms, cabbage ( or anything in the cabbage family), onions, peppers will often give a strong distinctive flavor which you may not want in the finished product . For example, if your making a tomato based soup, but you are using a veggie stock that has a heavy cabbage, mushroom flavor, it will transfer this flavor to the soup ( which you may or may not want). Something heavily spiced ( like chili) often will over power mist flavors.
For consistency, I use a the "vegetarian bouillon type product". The better than Bouillon is one option, I use another that is a " vegetarian chicken consume bouillon powder". And again, I use it for consistency, cause unless following a specific recipe to make a veggie stock, it will be different every time.
Being a vegetarian and an avid gardener, I eat a lot of veggies and have a lot of veggies available, so Im often just making a stock with what's available, or scraps from cutting up the veggies ( like celery tops, onion and carrot ends, chard stems, mushroom stems ...., whatever I can get my hands on). I salt it as if I were making a soup, and often use that alone as a base for a soup ( usually just a throw together ' whatever is ripe in the garden soup'.
But once again, if Im looking for consistency, ill go to the powdered stuff, cause I know its going to taste the same every time, same salt level every time, therefore very repeatable every time.
What I learned from Jacques Pepin , and others here on the forum, as you use your veggies, just toss the craps in a container or ziplock bag in the freezer. ( celery tops, onion, carrot ends ). And once you have enough, just make a stock out of it, then that can be frozen for later use. basically will cost nothing since you were going to throw out the scraps anyway.
( I also use the scraps for composting and feeding the chickens, so that's why I usually dont have too much left over)