I find that having good camaraderie with the other players helps significantly, so even when no one is posting and there are IC "dry periods" you're all still keeping in touch and up-to-date and the role-play does become the game that it's supposed to be, and everyone is having fun. 

I never put limits on post length or time it takes to post because that puts pressure on the player to meet a certain standard that they might not always feel like meeting (what, are they getting graded on it?), I only ask that people remain active OOC even when they don't feel like posting just so we're all up-to-date with each other. It creates a friendlier environment so people are less likely to simply disappear/dropout on the notion of "oh no one has posted for a while I guess this is all over why bother."

Edit: 

In response to the OP I don't really mind the segmented sections because you can always post the interest check in the general interest checks instead of in the section that you're looking to have your RP in. If you go by the guild rules regarding the sections then it really just becomes more about the quality of the story/plot/characters than overall length. I mean, all you need to qualify for advanced is "Three good paragraphs" and most people do that in Casual already.