Want to get good noise reduction on my Nikon D200. New camera or tweak the images?

I have a Nikon D200 digital camera; I think the manufacturing date is 2005 or 2006, which is ancient history in terms of DSLRs. This model is known for having high noise. I have really good noise reduction software that seems to take care of it (maybe with some image softening). If I get one of the new generation Nikons that generate less noise, would I get much better results than using my workflow method with my D200, using noise reduction software when needed?

Your camera can be outstanding on the noise if you learn to expose properly to prevent noise.
Read on Expose To The Right (which is left in Nikon.)
If you slightly overexpose and reduce in raw processing you reduce or eliminate your noise issue
As for noise-ware programs Nik software makes a great one that is either stand alone or photoshop plug in. Photoshop CS5's adobe camera raw is phenomenal on noise removal.

The newer generation Nikon's (starting with the D300 and D3), are better with respect to noise compared to the earlier models like the D200 and D2. Some have said the difference is at least one stop, may be two, between a D200 and D300 before any noise reduction is applied. Without knowing the software or steps used in your current workflow, I can't tell you how much better your final results will be but, given the fact you'll need less noise reduction, you'll certainly see less softening and therefore sharper images.

If you decide to replace your D200, the D300s is its current replacement but a new model is expected to replace the D300s itself soon. In either case, you'd have the benefit of a camera that largely feels the same as your D200. Having said that, there's also the D7000 which is cheaper than the D300s and actually offers better image quality than the D300s (itself better than the D200) due to a newer generation sensor and image processor.