When all is down, I have to say you are 100% correct on this! There is just one thing that I want from the D300 that I can't get from the D200 and that is the better IQ at high ISO settings (ISO 800 and above).
I hate to shoot with flash, it is just my style and the D200's noise is really horrid as you start to approach ISO 800

.. other than this one little issue I see nothing wrong with the D200 at all.
In the 4 years that I've been shotting DSLR I've only had dust issues on my sensor a couple of times (touch wood) and that's after more than 250,000 shots taken in these years and God-knows how many lens change. So, I am not all too worried about this, and not too keen on this feature on the D300.
As for the D3, there is no way I can justify that price to myself. Don't get me wrong, it is worth every penny and it's a marvel of a camera, but I just can't see myself spending that much on a DSLR body when I could spend that amount on so much more kit (I have a wish list, for photography items that go over £10,000; and this doesn't enclude my other hobbies and obligations

).
So, the question is, should I splurge £1,000 (or thereabouts) on the D300 to get the better IQ at higher ISOs, plus the extra ISO hitch to 6400

? Or should I spend just the £100 for Noise Ninja and do with some PP ... of course the £1,000 (or £900 after buying Noise Ninja) will be spent on something else.
Finally, it has been my style that I only upgrade models when my existing camera needs servicing. When my D70 needed to go to service, just a check-up, that's when I bought the D200 and the D70 became my back-up (which has since been replaced with a D40

). May be I will hold off until I need to send my D200 for service and then buy the D300?!?
See how confusing this is, and why I want to not think about this for a while :bang::bonk::bang:.