Picard's final statement seems straight out of Hume, who (if second-hand memory serves) felt that, as societies became wealthier, people would spend more of their time in contemplation.

Even so, I can't see getting around at least a unit of account: at some point, Starfleet will have to make a decision about commissioning a new space ship. To do that, they'll need to know what they could be doing with those resources if they didn't build a new ship. Thus, they'll need to know what it would cost them in foregone opportunities. To answer this, it's a convenient to have a single metric.

Ah, but that is Starfleet. Latinum is the universal currency in the Star Trek universe.

can't they just "replicate" building materials and food?

Yes, unfortunately, replicated food tastes replicated. That's why you see them so happy every time they get access to some organically grown produce.