Anyhow -- I think the burn-posts probably aren't big enough to do anything anyways

Maybe, maybe not. I don't think it is easy to say what is the effect of taking around 2000 STEEM per day off the market, day after day. I can't agree it is necessarily insignificant. I also think that even if it isn't significant now, it could grow to the point where it is. The votes have increased roughly 2.5x in the past month-ish (which is why it started showing up more on trending), so further increases are also possible.

Extracting curation rewards without distributing author rewards. High (and low, but probably mostly high) SP users getting rewarded for voting on literally nothing rather than encouraging new users by throwing them a bone

They are being rewarded for voting at all, which is part of the idea of curation rewards (it is somewhat debatable whether this is actually a good idea, but there are also good reasons for it), but curation rewards for burnpost are very low, because many of the first votes (which would otherwise earn the highest curation rewards), are within 5 minutes (in fact within 2 minutes), which causes the curation rewards to be returned to the pool.

The design of curation rewards is supposed to be "neutral" in that no matter what you vote on, the same formula for curation rewards applies. The return of curation rewards to the pool for early votes is the system's way of trading off between easy votes (like burnpost, or taking a vote on an already-trending post) and votes which require more effort to seek out (hidden gems). The former earn much lower curation.

Right now if you vote for burnpost you have a choice of voting early and getting low curation rewards (because much of the rewards are returned to the pool), or throwing your vote on at the end (as you could equally do with any trending content with equally minimal effort) and getting low curation rewards because you are a late voter. IMO this makes for fair voting.

Isn't there a buyer for every sell transaction on the market?

Sort of. This is a common misconception. Of course there is a buyer for every seller, but the amount of external funds people are willing to invest in Steem is limited both for any individual investor and as a rate of investment over time. The more STEEM units that need to be sold, the lower the price per STEEM has to go to match with buyers. And go lower it will, because as you said, every seller has to have a buyer.

Over time there is probably another indirect negative effect which is when the supply being dumped on the market is continually too high for the amount of new money coming in, leading continual price declines, the willingness of anyone to buy STEEM is naturally going to decline (why buy something that you expect to decline in value?), which is a terrible vicious cycle. Excess inflation is a killer of the investment prospect.

I have no problem with inflation payouts that compellingly help Steem grow and succeed, since those also attract buyers, so they create demand to offset their own supply. However, when we have a lot of inflation overal and a lot of the payouts are just cookie-cutter milking or otherwise largely or entirely worthless to building or promoting Steem as a whole, it is just destroying Steem as a credible investment and ultimately destroying Steem (because as the price drops there are no resources for development, promotion or anything else).

maybe individuals should just buy the tokens that users are dumping at such a low price, and be happy that they scooped up a deal

You don't get to tell individuals what to do with their money, and what investments to make which, to them, appear unattractive. Moreover, even the people are willing to scoop up cheap Steem (which, BTW, at times includes me) have a limited budget to do so. Too much Steem being sold to into too little budget = no good.