I'm with Alan here - clean only when necessary. I use the same lens changing procedures that you do. The only additional thing I could mention is that I once read in an article that there was a benefit to storing the camera sitting upright or with the sensor facing down - to avoid storing the camera with the sensor facing up. I have no real evidence that this has helped, but I have had my D200 since December 2005 and I have used the damp swab cleaning method only once (about 6 months ago). I found that simply using a Giottos Rocket blower on the sensor occasionally would remove the easily-visible dust spots. (I didn't worry too much about tiny spots off in the corners of the frame.) It wasn't until a few months ago that I finally got a stubborn bit of dust near the center of the frame and so I had to resort to the swab method.
Of course, it is also entirely possible that I shoot a lot less than you do and my sensor is exposed to less dust.