I can come up with arguments for both sides of the decision.
That said, you have to understand that your present K200 has an extremely good CCD sensor, and all the new models have CMOS based sensors. What that means is that CMOS is easier on batteries, cheaper to produce, and tends to have more inherent noise. Cameras like the 645D have a CCD sensor, great detail, low noise, etc. Now, Pentax with the K5 appears to have figured out how to combine CMOS with very low noise. I just ordered one - but it has not been shipped as of yet.
I was looking at a lot of shots I took with my K100 (a 6MP CCD sensor), and they are indeed really good - low noise, great clarity, excellent image quality, and in many ways difficult to differentiate from my K20 shots.
The K5 is going into end of life. So for a new unit, this is probably going to represent the best opportunity for a really good price - however, you still really need to look for optimal pricing.
So, that's my take....