Nothing else afaict. The only crap there is that you see an advert after every two three answers. However they won't bother you if you can ignore them. 

You're right that we don't think about Quora much, but I can see how it's pretty similar.

Do they just have simple up and down votes for answers or do they have a bunch of other random crap like Reddit?

Undisciplined

Are Stacker News Rewards Too Salient or Are They Not Too Salient Enough?

I think it's not much popular in USA because reddit is all over there. It's very popular for discussions in India and Europe or in many parts of the world. I often find good content there, although it has almost nothing for Bitcoin related discussions. 

I'd have ranked SN closer to Bitcoin talk but I see SN has versatility in content like quora has.  