OK. A suit every day will do you no good and be noticed. In the long-run (after you've made the investment in your clothes and your education), it will not matter. It is very easy to spot bright and productive students seeking a Ph.D., although the bright ones are not necessarily the most productive.
Don't overdress. Your peers will think you are putting form before substance. The senior faculty will think you are trying to compensate for a lack of productivity. In either case, if you are a whizz-kid (publish a lot and bring in a lot of money) you can do whatever you want (within certain broad limits) and they won't sack you. Just don't sleep with their wives or girlfriends!
I worked on my "figure". I bought a Concept 2 rowing machine and have been a pretty dedicated rower, first losing weight, then for muscle development, now to keep things in place as I have a history of weight gain.
Otherwise: on redefining oneself. Clothes are a part of it. The general theme i have found that works to "act as if" you are the person you want to be in all aspects of your life.