Sometimes you just want a certain kind of thing, and you have enough money for it, and it makes you happy, so that’s not really a waste. If we talk about how things look on paper, in terms of cost to performance/utility/convenience value, there are lots of examples of “waste.”
Near the top of the list might be carbon fiber water bottle cages. They are only a few grams lighter and maybe slightly tougher than ordinary plastic or metal ones, at several times the cost. Full disclosure: I own a few Campagnolo carbon cages. I think they cost me around $120 on clearance, for two cages and two bottles. I don’t regret the purchase. They’re a very cool accessory; they just don’t stand up to financial scrutiny.
At a bike shop today I saw an Enve bike seat priced at $400. It is very light and sleek. Is it twice as good as a $200 seat? Almost certainly not. But it’s way cool. If you have enough money that you can buy stuff like this and not go without food and shelter… why not indulge?