I cannot think of a bike that I've bought new, except going back to my Gitane Tour de France - in 1973. Still have this bike; heavy, but still rides well.
The Sweet Spot in terms of cost/benefit is used stuff about 5-10 years old. But you have to be really careful, do your research, and know what you are getting into. Bikes depreciate 30% when they exit the shop door, and then there is no reason to be paying more than 50% of retail for a 5 year-old bike. Most 5-year old road bikes feature a worn our drivetrain (rings, cassette and invariably the chain), and sticky shifters. So hundreds of $ of replacement parts right there.
The ultimate sweet spot for road is a 5-10 -year old carbon bike (T800 or T1000 level frame) bike with rim brakes (discs: heavy, fussy, expensive and unnecessary), external cable routing, a BSA threaded BB shell, and a 10-speed drivetrain. 10-speed consumables cost nothing these days... I go through 3 chains minimum per year, so factor this into your ride economics. And, STI shifters where the cables exit from the sides of the shifters... cleaner, smoother shifting, as cable runs under the bar tape introduce extra friction, and the current shifters eat cables. Dura-Ace 7800: best mechanical shifting ever.
So a 10-year old carbon team bike (UCI level kit) with Dura-Ace 7800 will be lighter, easier to work on, shift better, and definitely less expensive to run than any of the current elite-level road bikes, unless you are willing to forgo discs, and still pay in excess of $10k for something new.