You're incentivizing spam by paying for up to 60 posts per poster each week. That's 10 posts a day with 1 day off. There's no way anyone that is writing this many posts is actually saying anything worth reading.
We have those in campaign that requires upto 40 to 50 posts per week, with that you can also say they're spamming because they just have 2-3 days off if they were to write 10 post each per day but spam isn't about the amount of post you have to write per week because you can spam while writing just one post in a week. You can write 20 post a day and still not spam. Spamming isn't subjective to the quantity of posts we make.
You can write just 25 post to be eligible for payment in the campaign you're participating in and all that you have written isn't worth reading so what's the point here. Nobody asked the participants to make 60 post, we said the maximum to be paid for is 60 so the participants are free to choose any number they're comfortable with making. We have set rules for the campaign and anybody breaking it or that of the forum (by spamming) will be punished. If the participants decide to ignore our rules of no spamming and having a minimum number of 150 characters that's their problem. We accepted them into the campaign because they weren't spammers so if the later turn out to be one, they'll be punished. Nobody is demanding 60 posts from participants, they can write more or less without spamming the forum.
PS: I'm always in support of an increase in payrate per post to reduced the workload and I'll always pass that message to the founder of projects but don't use quantity of post to judge post quality/spam.