As others have said, it's in different places for different people. One of my riding buddies is a corporate CEO who makes about $1.5 million a year (it's in his firm's annual report), and he absolutely believes he NEEDS two different $4000 bikes. My income's about 1/20 of his, and I'm completely happy with my Rambouillet, bought used for $1000.
When I turned 55, I was planning to buy a custom Rivendell for my midlife crisis. At the time, they started around $3000, a ton of money for a guy with two kids in college. I did a lot of research, and Rivendell was great about explaining what I'd get for the money over one of their off-the-rack non-custom bikes. At one point Grant Petersen, who owns the company, said you could get 95 percent of the function of a full custom for 50 percent of the cost by buying an Atlantis or Rambouillet. I bought an Atlantis frame and fork ($950 at the time) and built it up mainly with parts I had, and I've never been disappointed (the Rambo came later, after the kids had graduated).