Welcome! I don't really see a problem with using the camera at lower ISOs as long as it is working. It isn't really worth replacing, you can get a refurbished K100D body through the bestbuy website for $259 plus tax/ship. Same sensor (if you are used to the results and like the 6mp sensor you currently have), slightly large but with the added benefit of shake reduction as well, which is well worth the money. If you're in the twin cities area you should keep an eye out on the national camera website (
Home) which lists their used camera equipment. They can send it to any of their stores for you. A few weeks back there was a used *ist DL body only for $199, and currently a *istDL body/kit lens for $299 (though the bestbuy K100d price is the better deal). Good luck with your decision!
edit: I didn't see the notes you bought a K-x as well, so don't need to replace it! again I can't think of a reason you couldn't keep using it. You could probably get a reasonable price for it in the marketplace here as well, if not for you I am sure someone would put it in their bag as an emergency backup.