It's interesting that you mention character development as being easier for you in longer posts because I'm the exact opposite- I prefer to develop characters through interactions rather than like, introspection, so shorter posts that run together with someone else's are my ideal, though I tend to settle for interacting with my own NPCs. I think that's why I found RP to be easier and more engaging a long time ago, when the interactions between players were all in the thread (admittedly out of necessity because communication wasn't as easy as it is today). Yeah, they may have been shorter posts, but they moved the plot along quickly and where everyone could see as opposed to these days, where so much time is spent behind the scenes- writing, editing, perfecting, participating in these joint posts that take forever to see the light of day.
Hmm, maybe it's like- I'm not interested in taking the time to perfect my writing itself. I don't really care if the words aren't perfect, or the characterization is a little off. We can always discuss and hash things out in the OOC if it's not clear. I'm more interested in fleshing out characters and worlds as we go and taking so much time to do so kind of throws me off, since I'm not getting the collaborative experience when I'm dropping 1500 words on my own. I think of RPs as more of a draft than a final story, because when you're collaborating with a bunch of people- hardly any of you are going to mesh, or click, or whatever. There's work to be done between players as well as by players to figure out where you're going and how you're doing it together. I just don't think more words, more time spent editing, and posting less often is particularly helpful to that end.
Bang it out and keep on going is really it imo.