AJ just mentioned he was processing NEFs, I do that too. At this point the camera retains no more control over colour but the processing software does, and I find Lightroom does it better than the D200's onboard processor or CaptureNX ever did.
You will get an improvement. If you're talking about me saying in the other thread there's nothing to be gained I should clarify this is from a utility point of view. You will get slightly less noise, and slightly better colour. The images will NOT be any sharper which is often the reason people upgrade cameras especially if they are new to SLRs. The question then becomes is it worth spending $1000+ on slightly better colour, or a new lens which may be sharper, have less CA, allows you to shoot in more conditions, etc.
Even with a 6 megapixel sensor modern GOOD lenses will only just outperform it. And I assume if you have a D50 you haven't got any $3000 lenses on it.
I have minor bias here, I don't care about noise or colour as much as the art itself. Photography is more to me than the clarity of the result, and one of my favourite pictures from the Time Life books is grainy as heck.