Advantage of the K-x is not just in it's better high ISO IQ. It uses newer technology, the K200D came out at the beginning of 2008 while the K-x came out in the late of 2009, almost a full 2 years apart. Which of course the K-x would have to be better in other ways too, it's got higher FPS, HD video recording, better auto focus, and probably some more other things.
But as for making the switch, if you're still happy with your K200D in comparison to today's newer cameras, then keep it. Otherwise if you're unhappy and unwilling to stick to your K200D based off today and in comparison and contrast with the newer cameras, then switch to the K-x.
From what you're saying, you're quite happy with the K200D and yet not quite as happy with it's high ISO. Now is the high ISO in the K200D still usable enough for you? Is today's new camera's increase in high ISO that significantly better, in that you will need to upgrade? If so then the K-x.
Just make sure that you are making the right decision because I know what a hassle it is to switch to new bodies all the time, I would hate to sell off my body after only 2 years of usage and waste more money to upgrade. But that's just me because I'm not that rich like some people. But overall if you are willing to to sacrifice then do so, if the amount of technological changes in the K-x outweighs the amount of technology your K200D boasts now in comparison with cost-advantage, then do so.
In the end it's really up for you to decide. We don't know how much you make, we don't know what else you buy, we don't know what your life decisions are based off of. Just ask yourself: Do you use high ISO enough that you will need it? Is the amount of high ISO pictures you take really that bad to you? Or is the majority of the images coming out of your K200D in higher ISO's good enough for you? Or do you just want the K-x just because you want a new camera, and is not necessarily going to improve what you take in terms of cost and the money you will lose?
Last edited by LeDave; 12-15-2009 at 10:48 PM.