Thanks Andy,
Well, I took the plunge and ordered the 400D. I've only had it a week or so, and haven't done a proper field trip yet. However, I've done some basic night test shots in my garden and drive etc. Early indications are pretty encouraging. I'm using the Canon with the Tokina 12-24 F4 ATX Pro lens. I've always been impressed with any Tokina lenses I've tried and this one is a corker! I'm usually pretty scathing about zooms but at 12mm and f5.6 the corner detail is really really impressive. I don't remember using any zoom of this quality before. Hopefully with a lens this wide I should always be able to focus by scale.
The Canon body appears to work well with my Nikkor 135mm f2.8 AIS (using an adaptor) so I will be able to recycle this item. Sadly my ultra-fast Nikkor 28mm doesn't appear to work well on the digital so I must reserve this lens for film ;-(