I'll go over my thought process below, but bottom line, no matter how I look at it, I just don't see a way of using payout minimums to stop spammers without also stopping new people who can't buy SP from using the platform legitimately.

A better approach seems the one SteemPlus is using, where they mark people as human, bot, or spammer. Once that classification system has enough data to be reliable the penalty for being marked a spammer could be to simply hide all your posts automatically, so that no one can even waste an upvote on them.

MY THINKIING
It's helpful to separate the discussion of posts vs comments. The goal is to fight spammers without penalizing newbies who can't afford to buy SP, so are working off the free delegation for the months it takes to grow that.

COMMENTS - If we look at the comments on this post, which has a number of high SP Steemians interacting, we see that not all the comments on here would get a payout at even the .10 threshold. Yet all but one of the comments I've read are clearly not spammers. If we increase the threshold to .25 we see that almost none of the comments on even this "well-healed" post would receive payouts. It looks like a handful that would.

We can anticipate that comments on the posts of newbies, the people who must desperately need to build an audience of readers and commentators, would receive even less because the people reading them tend to be other newbies. Asking someone to get 10 upvotes on a comment before they can expect a payout is like saying "don't expect to make anything on your comments unless you only read Whales or at least Dolphins."

The vast majority of comments on my posts get only my upvote. And I don't want to have to use a 100% weight upvote on every comment just to get the person paid something, which is about what I'd need to do given my current SP to meet even a .10 threshold.

So basically, I don't like the idea of raising the payout threshold for comments just to try to thwart spammers. I'd like to use a method that doesn't destroy the earning potential of newbies, either for commenting themselves or rewarding those who comment on their posts.

POSTS - Here I don't as much mind a threshold of some amount, because the person first has to get people subscribed to them. To do that they probably need to post something of quality somewhere at least some of the time. And only their own followers will see their posts. (Well unless they have money for bidbots and if they do, none of these 'payment threshold' approaches are going to stop them.)

So to say that a post needs at least .05 to payout seem reasonable to me. Basically you have to get at least 5 people who have a penny upvote to upvote your post. Since most newbies don't even have a penny upvote right now and it takes 2-3 of them to reward a penny, that effectively means that 10-15 other newbies have to upvote your post with 100% voting power for you to get anything.

It's still a tall order for many people I know. I see often people write very good posts, but only get 2-3 upvotes. So for posts also, this is not the way IMHO.

edit: I came across an example after leaving this comment that I think really makes my case on the posts issue. Here is a post from someone who's been consistently writing quality posts and leaving quality comments for about 4 months now, @eugenekul. I think this is a very high quality post, but before I upvoted it it had only .04 on it. If you look at his blog list, you'll see that most of his posts get less than .10, yet I think he is very much the kind of writer we want to see on Steemit, but clearly he can't afford to buy SP or even buy delegated SP. He is one of several examples I see that convince me that it would be best not to erect barriers to keep out spammers that really just keep out poor writers.