Regardless of how much I spend on a bike, I immediately start looking for ways to improve performance. In the past, I could always find a replacement component that would shave a few grams off the weight. Unfortunately, that type of upgrade didn’t improve my performance much, if at all. And in many cases the new light weight component was less reliable. It just wasn’t a cost-effective way to improve performance. However, recently after upgrading to tubeless tires I’ve had a noticeable improvement in performance.
Normally, I would ride a bullet proof tire like Continental Gator Hardshells to avoid flat tires. Although I rarely got flats with these tires, like most puncture resistant tires they have a high rolling resistance. After replacing my tires with Continental Grand Prix 5000 TL tubeless tires with a much lower rolling resistance, I gained a noticeable improvement in performance. In my case that is equal to about 10% of my average output of about 120 watts. See Continental Gator Hardshell vs Continental Grand Prix 5000 TL at bicyclerollingresistance.com for tire rolling resistance details.
Although puncture resistant tires reduce flats, they can’t repair a puncture on the fly like tubeless tires. See Ignorance is Bliss. Tubeless tires are the best of both worlds, they are reliable and offer great performance. I don’t think you can find a more cost effective performance upgrade for your bike than tubeless tires.