Do you rate discussions you didn't responded?

I usually do not. But as for discussion on which I did not subscribe, that is a different matter. You are talking about two different things -- one reading a discussion, and not responding to it because either you cannot know an answer or an answer will get you flamed or insulted, those I do not reply unless it is to uphold a moral principal, but I will answer those who I have not checked off as an interest, if it is something that I know about and can give advise on.

I do most of the time. I am not sure if it boosts up anything or gives me more money, but I find it the nice thing to do. If I take the time to stop and read it, I might as well rate it to :)

I don't rate a discussion unless I have responded to it and it needs a rating. I will leave the discussion for others to rate that do respond to it. You have a very good question though.

No, I don't really. If a discussion doesn't interest me, I feel like anything I would do to participate in it would be more harm than good. I would just be writing to get my four lines in, or the tick mark for the post, or hope that the person who started the post reciprocates and rates me well down the road. That's not me and not what I am here for. If I don't feel the topic interests me, I leave it alone and move on to the next. Its not fair to the person who started the discussion or any of the posters that did find it interesting.