I agree with you -- decades of psychological research show that people acclimate to what they have, and then want more.

Imagine cavemen postulating about what we'll do when we have these big machines that can carry us around at great speed, and when our food is already made for us and no hunting is required. Could they have guessed we'd work in glass office buildings so we can buy iPods and McMansions?

I suspect we're in no better position to guess how we'll use our future economic output, only that we will definitely want to spend it.

Wealth has increased enormously over the past couple centuries, but, as you say, we've absorbed it. But at some point as the curve trends up, we'll be able to work less and have more anyway on a year-to-year basis. Even though scarcity will technically never end, it might still feel like you can do anything you can imagine, for average levels of imagination.