The problem with extrinsic motivation is that, well the moment someone gets that reward, they either want more rewards or they lose interest.
As an experienced user, and someone who's seen the rise and fall (or at least the slow decline) of internet communities there's two factors here.
A stagnant community community is unhealthy. People leave, they lose interest. In a long running set of communities like this, well, people even die. As someone interested in various communities in SE, my intrinsic motivation is having these spaces thrive and grow.
I don't need a COC to go "hey, this new user's post could use a little love." or even better "This post is terrible but the tool he's using is really cool and by improving the post with the stuff I've learnt over the time I've been on SE, it can be more useful".
In a sense building a sense of community and shaping that intrinsic motivation to improve posts is important. And the way to do that really is to engage folks and have them.
That's to say, it would be, but at a less obvious level.