I recommend a splash of Maggi seasoning. Low salt it isn't, but it's so concentrated that an almost imperceptible bit can really transform the flavor of a sauce or soup.
Deglazing works with veggies as well as meats- if you roast vegetables and then deglaze the roasting pan to make your sauce, scrape it well and the browned bits of fond will give your sauce infinitely more depth, whether you deglaze with wine, vinegar, cream, or broth... My apologies for pointing out the obvious if you've already been doing this.
Smokiness can be a big flavor boost too. Some good smoked paprika can add a lot, especially to legume-based dishes or nearly anything that's creamy or starchy. I sometimes use Liquid Smoke in vegetarian beans or chili, to take the place of bacon or fatback. A little bit goes a long way- I use an eyedropper.
Better ingredients make better sauces. Secret ingredient for a good wine sauce? Good wine.
Last year I upgraded my go-to soya sauce from Kikkoman to Wuan Chuang and it's made a noticeable difference everywhere I use it. Same thing to a lesser extent with choosing a good quality balsamic or Chinese black vinegar over one of the plainer vinegars.
Along the same line of better ingredients, someone posted awhile ago that you can give many dishes a subtly improved quality by using shallots instead of garlic, leeks instead of onions, and fennel root instead of celery. I can't take credit for that one but the idea is sound..