Yeah, sometimes we get a little adamant about Nisus, just as Melell users sometimes do the same for their product. I have a crush on Nisus, I must admit. But, for as much critical distance as I can muster, that is why I was also sure to say that NWP is by no means perfect, which as you've seen its users can also be very vocal about in these forums.
I am interested in knowing what you think of Scrivener. I've been using it for some complex papers I've been writing, and have found it to work nicely at just what you described -- the sort of unstructured writing that requires all parts of a work to be movable. It also does a damned good job at managing references and other media, as I can have a full PDF of an article, its citation information from Endnote, its abstract and my own personal notes on it, and on top of this, I can import full sound recordings of interviews that I have transferred into digital format, images that I plan on using but don't know where just yet, and everything else right in the document that I'm working on and all of them are ultimately usable in a productive way. Because of this, I have found it more agile in the beginning (and even middle) processes of writing scholarly articles than anything on the market. In addition, it has a split pane writing interface where you can work on two different parts of any fragment at once. This is one thing that no word processor (or even an outliner to some extent) has allowed me to do successfully, and one that I don't think they're really set up for - inevitably they force structured and linear writing on you, although to be honest, I've never used Melell's outlining features because I was one of those people who couldn't crack the interface to even get there in the first place. Scrivener takes about 15 minutes to learn and is as intuitive as NWP. Scrivener is not for final document creation, but what it does it does so well. Together, along with Endnote, they are my toolbox (along with Pages for syllabi and anything involving complex images, media, etc. and Keynote for stunning presentations and lectures, and Numbers for gradebooks and any low-level numerical analysis, which luckily as a qualitative researcher I rarely deal with).
None of these tools is a swiss army knife. They all do their things and they do them well and they all play their parts at specific times of the writing process - Scrivener when I want to make a mess, Nisus when I want to clean it up and get it into its final format. That was the hardest part of moving from Word for me, which does a lot of things and none of them are actually implemented in a meaningful and well-thought out way (2008 has only made this more clear). I had to learn a whole new, but ultimately smarter and more intuitive and much more productive, workflow, and ultimately it is my workflow and no one elses -- so your mileage, it should go without saying, may vary.
And if I get evangelical over Nisus sometimes, well...that's just puppy love.

Scott