njkayaker

This is a false dilemma. It's not a choice between McDonalds and Spago.

We'd have to look at the actual costs. A meal at Spago might be as expensive as multiple meals at some other very-good restaurant that isn't as "fashionable". That is, it's quite possible that one could get more enjoyment at going to some high-quality place other than Spago. (It's quite possible that one reason people go to Spago is to brag about it. There is nothing that establishes that one has to spend that sort of money to get the same level of quality.)

Things like Spago are really targeting people who have money to burn (the wealthy). For people of more limited means, there are, almost certainly, more effective ways to spend that money (ways that would provide much more enjoyment for the cost).

People are free to spend money on whatever they want. That, though, doesn't really mean there's a rational reason behind it.

As a general principle, this is false since typically people are poor judges of what "makes a difference".

You are ignoring the cost. A rational decision is based on benefit and cost. If you are wealthy, then cost really doesn't matter but, I'd guess that most people here are not wealthy. It would be unfortunate if people thought that spending money on Red and Dura Ace was necessary (it isn't). And, of course, 105 is very good (Dura Ace might be better but it's only a bit better for a lot more money).

Some people buy things for style (it's their choice!) but too-commonly rationalize their purchase by arguing that they get unrealistic performance benefits. It's the rationalization that is bad (it's dishonest and leads to other people being misinformed).