The value of USD is imaginary, because if I gave you a bill of $10 USD all I am giving you is essentially paper with a 10 written on it. It is an imaginary number, but what keeps it going is that everyone agrees to keep using it to buy or sell, which then those who issue it devalue, and so causing the population that uses it to become poorer.
I think we are using different definitions of imaginary. But rather than dispute that, I think the real issue is this
"...which then those who issue it devalue, and so causing the population that uses it to become poorer."
As the currency is devalued relative to a commodity, say, flour, it is also devalued relative to labor.
Here's what I mean.
Suppose 20 years ago a bag of flour cost $1. And minimum wage for a worker at McDonald's was $3 an hour.
For ease of math, let's say that same bag of flour today costs $2. And our McDonald's worker now earns a minimum wage of $6 an hour.
20 years ago, the worker had to work 1/3 of an hour, or 20 minutes to buy the flour.
Today, the same worker works the same 20 minutes to buy the same bag of flour.
So although the price of flour has doubled, the worker buys the same amount of flour with the same amount of labor.
That's a very simple example, of course. In real life, there are loads of factors that influence prices.
There's an interesting situation in the world of electronics, like laptops and cell phones. The amount of labor that it takes today to buy a device with a given amount of computing power versus how much labor an equivalent device would have taken 20 years ago is far less. In other words, when it comes to electronics, people today are far wealthier than they were in the past.