I can only answer from my own experience as a reader here, but I must admit spelling, spacing, grammar, correct word usage, etc affect my reaction to Steemit posts. (effect or affect? Now I'm anxious and overthinking  my own words!)

It's 2 things for me. 

1) having limited amount of time to peruse my feed I don't want to spend extra time on a poorly written piece just trying to interpret what they are saying. And typos, spacing errors, lack of paragraph breaks, etc cause my brain to process it more/takes longer to get through. 

2) I only know English currently, and if I read a post that seems interesting but with struggling English then I think I subconsciously suspect I won't really understand the writer's intent anyways due to difficultly in translation. Like, I'm not going to really get what they are saying because they don't know English well enough to fully express their experience. So I'm less likely to finish reading it or upvote it. 

But please let me say this - I am not judging or complaining. I'm not saying that I look down on these posts. I can only humbly speak 1 little language. I have great respect for folks who speak more than one and who write in a nonnative tongue. I hope all being feel free to express themselves. I'm only being honest about how I often respond to really poorly done posts. 

This post has a few little errors, but not enough to deter me. I read the whole thing with interest, upvoting, following you, and posted a crazy long comment. ;-)