An NIE like this doesn't get declassified to any extent unless the administration wants it. Why now?

No kidding. I'd go further, and point out that this is clearly not a real NIE, but something produced entirely for public consumption. Note that the first five pages, of nine, introduce NIE process and terminology. No official who routinely reads those would need that.

Earlier this evening, I saw Pat Buchanan (don't remember which show or even network; that guy really gets around) theorize that it was released so that Bush could "walk back the cat", by which tortured simile I think he means that it's a face-saving way for Bush to back down from his belligerent rhetoric. Sounds as reasonable a guess as any other.

Why would Iran suddenly decide in 2003 on their own that they would rather not be pushing a nuclear program? Think about it.

Read about it:
Our assessment that Iran halted the program in 2003 primarily in response to international pressure indicates Tehran’s decisions are guided by a cost-benefit approach rather than a rush to a weapon irrespective of the political, economic, and military costs. This, in turn, suggests that some combination of threats of intensified international scrutiny and pressures, along with opportunities for Iran to achieve its security, prestige, and goals for regional influence in other ways, might—if perceived by Iran’s leaders as credible—prompt Tehran to extend the current halt to its nuclear weapons program. It is difficult to specify what such a combination might be.

The neocon jackass on the show with Pat tried to spin it that it was the invasion of Iraq that did it, which seems to be where you're trying to go with it. You're both welcome to argue with the DNI about that.

One of the points asserted in this talking-head piece was that Bush knew a couple of years ago that his rhetoric about the imminent threat posed by Iran was highly exaggerated. There seems to be some corrobation of that assertion at the end, where it compares this NIE against the one in 2005 (another thing you're unliikely to see in a genuine NIE). The projection of when Iran would be capable of building a nuclear weapon is unchanged, though the latest version is more verbose about saying the same thing:

We have moderate confidence in projecting when Iran is likely to make a nuclear weapon; we assess that it is unlikely before early-to-mid next decade.

Not exactly an imminent threat.

But, as you say, why release it at all? Could be a way to back down while saving face. Could also be intended to influence the Presidential election. Note that the absolute earliest projection of nuclear weapon capability, qualified as virtually impossible, is late 2009...after the presumed Democratic President takes office.

Sure enough, the neocon spin doctor tried to spin it into a threat that if we elect a Democrat, we're all going to die in a mushroom cloud labelled "Made in Iran".

There's definitely more to the story of the release of this "NIE" than meets the eye.