I leave the fat on the stock, and when I decide to soup it up, then the rest of the flavorings you suggest are used. It heats enough to get those flavors then the veg is discarded and the onions and carrots and whatever are going to stay in the soup are then sauteed and added to the stock.

In the US it used to be difficult to find no-salt vegetables. Now they're pretty much everywhere and don't cost more than their salted variety (fewer ingredients but they have to use a bit fresher food and process it separately.) Salt can disguise some quality issues. This is why I also use frozen vegetables sometimes; they are frozen closer to the field and are usually picked closer to ripe when used for freezing. I use a lot of frozen strawberries because those fruits didn't get as much of the nonsense as the big beefy flavorless berries that appear fresh (probably picked green and ripen on their way to the store). Frozen fruit is usually smaller, riper, and better tasting at the time it's frozen.