I think that sounds fine though. You could consider HN to be "like reddit" too, but there's still value in HN.
It is Quora itself that needs to justify against that valuation, not anyone else. Where that is fine or not, I think the news itself is self-explanatory.
I'm finding it hard to think of other domains with succesful quasi-public institutions run by for-profits without monetization. Are there other examples?