Rather than bouillion cubes, I think I would buy a pack of screw top jars and make your own veggie bouillion, and store in the frige for use in cooking for the week rather than using veggie bouillion or broth from the store.
As a non vegetarian, I make my own chicken and beef broth to avoid excess salt, phosohorus and potassium that manufacturers add, primarily as preservatives and flavor enhancers, and which are not well documented on labels. There is very little protein in the broth I make, but it is not vegetaian. If anything, I find commercial vegetarian broths have more rather than less of this crap than meat broths in the attempt to make veggie broth taste like meat broth

The reason I mention this in a vegetarian thread is that I can't vouch for the following recipe. but is rated five stars:
http://www.foodnetwork.com/recipes/basic-vegetable-stock-recipe.html
I am not fond of rosemary. I would add fresh parsley instead. And I like browned, chopped portabello mushrooms in broth.
I like that the recipe has variation, based on what fresh vegetables are available.
I agree fully about avoiding store-bought bouillion for the exact reasons you gave, but to be honest I think that making broth or bouillion or stock is one of those areas where the straight-up veggie adaptation of the meat-centered item often results in a more time-consuming and less satisfying result. Making meat broth makes sense: the meat comes out tasty, and you get good use (and nutrients) out of the otherwise useless bones. I personally have never been a huge fan of making veggie broth the same way, mainly because I feel like you're just wasting the vegetables. If I'm going to roast a pan full of veggies in olive oil (delicious), I want to eat them right when they come out of the oven rather than boil them until they're dead.
So here are some things I like to do for veggie soups:
1) If the broth is the star of the show (like in matzo ball soup), I like to sautee some combination of garlic, ginger, mushrooms (reconstituted dried shiitakes are convenient, but fresh are great), and chiles (either fresh or dried) in olive oil in the bottom of a stockpot, along with some combination of carrots, celery, and onions (or whatever's in the fridge), and then add water and salt and pepper and simmer for about 15-20 minutes. The short cooking time means the other veggies are still tasty, but the broth itself is flavorful because the shiitake, ginger, and chile flavors are so strong. (For matzo ball soup, I remove the veggies before adding the matzo balls so they don't get overcooked, then add them back in at the end.)
2) If the broth is not the star in and of itself, but I'd still like some more body to the soup, I'll use either leftover chickpea cooking water (hey, I was making chickpeas anyway so why not save the liquid) or kombu dashi. Kombu is a dried seaweed you can find in Japanese grocery stores, and making dashi (broth) is as simple as either letting it sit in cold water for a day, or near-boiling water for about 10-15 minutes. The dashi doesn't taste like much in and of itself, but it enhances the flavor of other ingredients (and also helps beans break down and cook faster). I like using dashi for Asian noodle soups and chickpea cooking liquid for one-vegetable soups like cauliflower soup or cabbage soup.
3) If I'm making a full-bodied, full-flavored stew like chili or pumpkin stew, I really don't need to start with broth or stock; I just use water (and maybe some wine, depending on the soup). A lot of recipes that call for stock or broth taste just fine when made with water.
4) The world's easiest broth is miso soup. You can now buy little tubs of miso at Trader Joe's or Whole Foods, not just Japanese groceries. They keep in the fridge for months. Just scoop out a tablespoon or so, add it to a cup of hot water, and stir. If you like, you can cook it on the stove and add other ingredients to make it more of a meal (tofu, noodles, veggies, seaweed), but you can also just drink it in a mug like tea.
I should also add that I'm allergic to soy, which is why I don't eat miso the way I used to (it's made from fermented soybeans) and also don't use soy sauce in Chinese cooking (yeah, I know, what kind of a Chinese am I), but a bit of soy sauce goes well in all of the above options. And you can put ginger in the kombu dashi, or kombu in any of the stocks - the mix and match is completely up to you. Anyway, just thought I'd throw these suggestions out there, in case the long cooking time of the Food Network recipe scared anyone off. It can be made to work in a busy schedule if that's what you crave (make a lot at once on a weekend, reduce it, and freeze it), but I just wanted to share some quicker weekday options that don't need to be made in advance.