shoes: Shoes really do make a difference. I do think it is worthwhile to try a lot of different brands to find some that work for your feet. I can go up to 2.75", but there are some really good looking and professional kitten heels around. Too round of a toe will look stumpy and/or casual, so look for a more almond to slightly pointy toe. My preferred brands, which may or may not work for you as we are all different: Cole Haan with Nike, Rockport with Adidas, Sofft, Calvin Klein, Coach, Clarks (Privo or Artisans line), Ecco, Born.
Sounds like you have a good assortment of basic bottoms. Instead of cardigans, look for some interesting tops in patterns. Banana Republic, Old Navy, Target, Boden.
Accessorize. This blog post is pretty good:
http://www.bridgetteraes.com/2014/03/30/how-to-look-stylish/
A few inexpensive necklaces and a few scarves can definitely punch up your wardrobe.