You can never go wrong with a basic beef stew. I basically make my crock pot beef stew the same way that you do, although I don't brown the beef and use flour to thicken the stew. I just chop the onions and throw them in with the other ingredients. Worcestershire sauce will kick up the flavor. I began adding tomato paste a few years ago. I squeeze about 2-4 tbs from the tube. Some people add a 6oz can of tomato paste, which is a little too much for me. The tomato paste not only darkens the stew a little, but does add flavor and enhances the beef taste without overwhelming it. You'll notice the difference just as you'd notice the addition of bay leaves to the stew.

A vegan technique to thicken soups and stews is to use a potato. You can either add an extra potato or two or just remove (or leave in crock pot)and mash potato when soft and return to pot. It does thicken the stew.