I do, but for one main reason, if I write something that I think is particular well done I like getting upvotes, not necessarily because of the payout, but because the post is higher up on the 'hot' and 'trending' threads on Ecency, meaning there is a better chance of people reading it. High payouts don't necessarily mean people will read it, but there is a better chance of getting eyeballs on what we write. I could be wrong, but from what I see, large payouts = more exposure

Especially because 'hot' and 'trending' tabs transcend communities, and through those tabs I've met people and read things that I wouldn't have seen if I just scrolled through the communities I follow.

Secondary reason would be increasing my stake, even when I don't have much money to put into my account.

In regards to autovotes, I've often said that certain people could write about going to the toilet and get a massive payout, but as you said, most people like yourself in that position treat posting with responsibility, and that is clear, there are plenty of people here who could post daily if they wanted to.

In regards to how many people would post if there were no rewards, I think there would be a large drop off, but it's hard to judge