The thing is is that you cant rush activity though. You can only bide your time to collect it.
True signature campaigns should be using this techniwue and paying people with higher activity rather than post count.
They do pay people higher by activity. I think all deals do this and there's ones that pay for a minimum 50 posts rather than per.
Generally speaking, accounts with a higher rank (higher activity) get a higher payment.
Some programs pay per post (eg. PD), some pay per activity point (eg. BitMixer), some pay the same amount as long as you meet the min requirement (eg. GAW for 50+ posts a month).
For details, you'd better check https://bitcointalksearch.org/topic/overview-of-bitcointalk-signature-ad-campaigns-last-update-01-jan-23-615953
But it's necessary to keep things in control. It's just a pity that new people cannot be "reviewed" to be fast tracked to senior levels, based on there background and knowledge on the subject. 
), but usually it dies down and I end up mostly lurking. Oh well. 
. The fixed deals also probably cut down on spam, but the operators don't get as much advertising as the pay per post ones. Maybe more deals will change to the fixed rate model with the price rises and stuff. At least they can budget how much they're going to pay out if they cap the number of participants too.