Where I think the value comes from is that people are putting in value that they in the past was trying to hoard for example inside a bank account. And that it seems like you get a higher return on investment by investing value into other real humans instead of a stock.
The way I see it is that we have lots of value that is just sitting and we aren't using it. If we can give it away instantly to someone else then the value was always there but now it's being used more optimal to maximize it's objective. Like we are streaming music on Spotify we are now streaming value with micro transfers that are optimized by using the precise range we think is fair.
As I have seen @nanzo-scoop talk about the real currency is more hidden and that is our Time and Attention. If Steemit can attract our Time and Attention with real value creation then other more surface layer currencies like Steem Dollar and Steem will increase in value. But the real value is when people invest that Time and Focused attention.