Position, Training, Nutrition, Rest, Kit...IMO this is the order for performance improvements.
Good aero wheels offer the biggest increase of speed compared to the rest of your kit...but...there are some caveats such as they are a pain to get up to speed for the lighter rider, can be difficult in side winds...not "can", they are a b itch in side winds, dragging them up a climb is not a lot of fun.
I'm not knowledgeable about supplements but back in the '90's I experimented with Creatine for one racing season. I increased my weight by 5 lbs average...I went from 135lbs to 140lbs of muscle...my thigh size increased and my sprints became much faster with far more power. I was generally a top 10-15 in the normal crit in New England before my experiment. I moved up to top 5 and winning several crits and primes. I even beat some of the best sprinters in my category...Masters/cat 3 at that time...After one big win several opponents/friends came up to me immediately after the race and said "what are you taking". I told them Creatine and they laughed and agreed.
Down side it hurt my climbing ability. Dragging that extra weight hurt my finishes in races with a finish at the top of a climb. And it was expensive...yikes !
When that season ended I stopped using Creatine and went back to my normal body size/weight. It was an interesting experiment.
I did not change my training plan during that season.