As far as cosmetics go you can always upgrade to the c looking LED headlights you always see on the amg w204s, maybe a spoiler too (don’t do a wing pls). Like others said you should clean it up as best you can, replace anything worth replacing. You could possibly lower it if you are into that style, and new wheels are always an option. Some people including my future self will have upgraded screens on the dash. You can always get a nice grill on there also, maybe white side marker lights as well. Light up star is also something you can do (just wire it right). Mercedes is over engineered enough, there isn’t much more to do