I agree that incentivizing activity promotes activity, that's implicit (and frankly explicit too).
But what I think is that while this 'economy' creates a different set of incentives apart from the natural ones that are inherent to the forum setting. You post now because, presumably, you want to; there's nothing that's pushing or pulling you away that is within your control, and so on some level you must find it fun, either because one find it legitimately fun, or because, like me, one is a lunatic who just likes hearing the sound of their own voice (even if it's entirely in your own head because you have to type everything out as opposed to being able to just say it).
Once you implement a system in which you're rewarded, sometimes, a bit, for this, then the incentive structure changes.
As an example; let's take Jim, a totally real person I didn't just make up. Jim likes posting a lot. But he's got other shit to do, so he can only do it in intense bursts, followed by lulls while he does his other shit, and then a fit of intense activity again when he has the time.
However, the incentive structure as developed (in this very real scenario I didn't just make up) rewards posts every two hours much more than a post every hour, and much more than a post every...say, 5 minutes. Jim is getting penalized, relative to a hypothetical individual who perfectly makes use of the incentive structure, which we'll term
That Which Has No Life. Perhaps that's simply a problem with the incentive structure being somewhat unfair; instead of that, you reword it so that if you have 5 posts per day, then each post is worth X ;if you have 10, it's worth Y, and so on.
But Jim works too much to have time on weekdays. He can only do shit on weekends. He's shot 5/7s of the week, and so relative to TWHNL, his progression is suboptimal. Well, maybe we can rework that, too, so rewards are distributed monthly, and based on an averaged daily amount.
But once you've divorced the reward from the actions to that extent, are you
genuinely still incentivizing certain patterns of behavior, or are people just going to keep doing what they were always doing?
Fundamentally, there will need to be a decision at some point between some arbitrary notion of fairness, and the ability to incentivize behavioral patterns.
And if you're not actually incentivizing behavior, then there's no point to introducing an economy; but on the flipside, if you
are incentivizing behavior, there is a real chance that some people will simply benefit inordinately (obviously not to the degree of TWHNL), and there may be complaints of unfairness which could act as a
disincentive, which flies in the face of the whole point anyway.