I think you'd feel better about buying a new bike to get something that has some cool new features that makes it worth it. My old bike was getting worn out, so I justified getting a new one by also getting electronic shifting on it. Sure, I could have put e-shifting on my old bike, but that bike is already close to retirement and electronic shifting is cheaper buying it on a new bike than buying it in pieces and then adding it. So I justified it by saying if I successfully completed a really hard race, I'd buy myself the new bike with electronic shifting as a reward and as my birthday present. E-shifting probably only saves a couple minutes because you are in a better gear more frequently, just like your frame might save you time, too.
In your case, I'd buy the new bike to get the fun factor of disc brake wheels (if you can also afford those new race wheels). A new bike every-so-many years keeps the athlete interested and happy. Testing shows you might go faster since you feel safer with the braking, too. Definitely so if you live someplace hilly and rainy.
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