1. For each topic, get a list of the distinct users who posted there in the last 24 hours.
I think this will give a terrible incentive to spammers to use more accounts to spam. I've created many lists, checking how many distinct users have posted in a thread. Typically, there are 2 kinds:
a. threads with hundreds to thousands of Newbies posting once
b. threads with a few dozen Newbies (or higher ranks) posting tens to hundreds of posts each
I expect b. to switch to a., making them more work to nuke.It took me a while to figure out these 3 points aren't meant to be separate ideas, but implemented together. That makes much more sense, and makes my initial reponse irrelevant.
2. Give the topic a score equal to the sum of each such user's total earned merit.
3. Sort by topic score descending, and secondarily by the usual last post time.
When you say "earned", does that mean you'll ignore the airdropped merit? If so: I like it! That's a great way to reward decent posters, and they have something to lose if they spam and get banned.
I've suggested it before and I'll do it again: can Newbies, Jr. Members and maybe even Members lose their ability to "bump" a topic on certain boards? They keep their freedom to post, but it will end most bump spam. And if they use higher ranked accounts to spam, they'll only have a limited supply which can be dealt with by banning them.
but it requires more resources to manipulate, at least, and newbies have no influence. Maybe it'd give certain users overwhelming influence, though.
Good point! I can already imagine the offers in my PM for one post in a thread, if it's sorted by total merit earned

That's the problem, just be deleted. Why should not punished them ?
I think Mods are too soft on spammers, especially compared to the number of spam bots that go around. I've reported many bump bots that just got a post deleted instead of a ban. Not only does that not matter to them, it's not even a punishment as the bump has had it's effect already.
For example, If I report 10 posts in one thread and they are marked as good, then the thread should taken down from the first page.
That can be abused to kill a competitor's thread.