Originally Posted by
downtube42
Upgrading to new parts has a poor payoff, aside from saddle. You're competing against OEMs who get a huge volume discount; you can approach new-bike prices by buying a groupset piecemeal. But upgrading to used parts is another story. Bike tech is changing so fast, and so many people want to be on that bleeding edge, that lightly used quality parts can be found quite reasonably, if one is patient and quick. Used narrow rim-brake tube wheels benefit from a triple whammy, with wider, disc brake, tubeless-ready on the bleeding edge. I agree the gains from the OP's bike will be small compared to, say, working on the engine. But some aero wheels could make an impact if the OP is fast at all.
I agree, buying used parts can save a ton of money. However, from my own experience, I would be leary of buying used parts from anyone other than someone I know well. Otherwise, you have no idea truly how much use/abuse the part was subjected to and you could be inheriting someone else's failed, or near failing, component. In which case you'll end up having to buy a new one anyway, on top of the failed used one. Having said that, I typically only buy new parts from reputable dealers and used parts from friends or people I know.