One of the problems in trying to objectively determine how much is too much, is that people come from different backgrounds. Meaning that a citizen of country X could be making 100$ a day and a citizen of country Z might be making 10$ a day. Now for the second one, most posts in the front page of "trending" or "hot" might be "excessive". So you have a real problem when subjectivity of one's own life condition clashes with what one wants to be an objective rating.

What you're describing is the exact functionality of the flag. It was right next to the upvote until a few days ago, and was just an upvote turned upside-down. If you want, just use the flag... there's literally no difference between what you're suggesting and the flag.

By my thinking, the purpose of upvoting and downvoting is for voting whether or not content 
is valuable or not valuable. 

The subjective interpretation of "what it should be worth" in dollar terms is vindictive and toxic. 

If we're doing that, I would prefer that the dollar amount be hidden from the UI.

I like your ideas to have two different types down votes.

I agree that having a payment down vote "to be used when you feel that a given post (or comment) has received a bigger payout than it deserves" will result in more accurate curation.

It also makes sense that there should be a separate spam/abuse flagging/down vote as well.

Separating the two eliminates confusion as to the reason for the down vote.
I think your idea, and @djleo's idea could be combined. He suggested that we gamify downvoting:  https://steemit.com/steemit/@djleo/proposal-drastically-improve-steemit-quality-control-with-incentives

I kind of agree. But it would be subject to greater abuse, perhaps being more trouble than it's worth. When whales come upon a post that is worth enough already, they simply should not vote for it.

If you don't think that a post is valuable (in your subjective opinion) then don't vote for it.

But to override the votes of those who (in their subjective opinions) think that the post is valuable or valuable to them? That goes a little too far in my opinion.

I think a downvote payment option would create a 'crabs in a bucket' mentality. Where people downvote posts to increase the share of their own content or content they like. 

If users feel a post is receiving a bigger payout than it deserves they should simply abstain from upvoting it.

There is an element of luck and timing that accounts for some of the large payouts on *supposedly* 'less deserving' posts. This randomness, whilst it may irk some, it will let others know that they could possibly benefit from this unpredictability. 

However in the long run, consistently providing quality content should yield consistent rewards, and people should not be overly concerned about the occasional post that wins the Steemit lottery.

Thats true good idea. Check out my ideas here please https://steemit.com/steemit-ideas/@nicholasparr/easier-to-share

Similarly, we could also think about *rewarding* those who downvote content for a valid reason (spam, plagiarism, etc.). Curation goes both ways as there is good and bad content.

That's the functionality of the flag already, you'd need more steempower to have a noticible impact though.