Thanks everyone for your responses. I'll go to the two examples I cited:

Non-urgent action (deadline 2 weeks away)
I totally agree this doesn't have to be done at a specific time (merely by a specific time), so in that respect, the Next Actions list does seem like its proper home.

But my BIG question here is: am I wrong to have a NA list that could be left alone for a month, providing I'm meeting my calendared commitments? (It feels like that's not quite right.) And if I do make my NA list a bigger part of my day (currently my calendar dictates 99% of what I do), how do I make it that way? Two questions to that:
a) can I integrate deadlines into Next Actions? Is there good 'formal' way of doing that - e.g. using the Due Date field in Outlook?
b) Should I be blocking time in my calendar purely to address Next Actions? This feels like the only way I'm going to guarantee getting round to them.

Courtesy reply
I phrased this badly - in the instance I was thinking of, the message merited a more substantial reply that would take way more than 2 minutes. To the point above, Next Actions is where it belongs. But where I struggle is this: it doesn't need a deadline, but nor would it be great to not get round to replying for several weeks. And under the way my current NA list works, that could happen.

It feels like the answer here is to have a Next Actions list that's much, much more prominent than it is for me now. But the thing I want to avoid is having a list of 'Urgent Next Actions' - that feels exactly like my pre-GTD to-do list that caused me a lot of trouble!

Thanks again.